This is a missing scene from Star Wars: Episode II – Attack of the Clones.
We jump into the story in the middle of the scene where Anakin and Padme meet again for the first time in ten years.

Padme drew herself up. "I don't need more security. I need answers. I want to know who's trying to kill me."
Obi Wan answered seriously: "We are here to protect you, Senator, not to start an investigation."
Anakin, who was almost curled up inside his Jedi robe, hands fisted into the sleeves broke in with a little heat in his voice: "We will find out who's trying to kill you, Padme. - I promise you."
Obi Wan stared at his padawan. "We will not exceed our mandate... my young Padawan learner."
"I meant that in the interest of protecting her, Master."
"We will not go through this exercise again, Anakin... - and you will pay attention to my lead."
Anakin shot back with a simple, rude: "Why?"
Incredulously Obi Wan gawked at the boy, "What?"
"Why else do you think we were assigned to her if not to find the killer? Protection is a job for local security, not Jedi. It is overkill, Master. Investigation is implied in our mandate."
Having regained his wit, Obi Wan tried to quell the rebellion with a short: "We will do exactly as the council has instructed." He added ominously: "And you will learn your place, young one."

The rest of the small gathering had been observing the exchange with obvious discomfort. Breaking the awkward moment, Padme tried to defuse the situation by saying: "Perhaps with merely your presence... the mystery surrounding this threat will be revealed. Now, if you'll excuse me... I will retire. I know I'll feel better having you here"
She walked out of the room as quickly as possible, feeling a little unbalanced by the unforeseen conflict between her two protectors.

After having checked the security measures, Obi Wan marched back to his private rooms in the Jedi temple. He didn't say anything to his apprentice, expecting him to follow without being instructed to do so. And Anakin did.
He was still stewing with a mixture of anger and embarrassment at being reprimanded in front of Padme of all people, when all he had done was to voice the truth. They had to find the killer.

When the door slid shut behind them, Anakin took a deep breath: "Master, you must see that…"
He didn't get any longer into his rant before he was cut off with a short: "No." from Obi Wan, who held up a quelling hand.
"No, my young apprentice. No more talking. I told you, you will learn your place. And you will. But first. We will meditate."
"But, Master…"
"I said, no. Meditation. Now."
"Yes, Master."
Anakin took the stance he preferred for meditating, well balanced, tall and proud, and closed his eyes.

Obi Wan's words were quiet but firm. "No, Padawan. Today you will not be standing for your meditation. Kneel. And meditate on your place. Feel the force as it connects us all and find your place in the rhythm of all things. Consider your error today and what you should have done differently."

Anakin stared at Obi Wan for a long moment. He hadn't been told to kneel for meditation in years. Not since he was a little kid, who couldn't stand still and kept fidgeting during the seemingly endless meditation periods his master insisted on every day.
Each day started with meditation and it had taken the active boy a long time to find the stillness and pleasure of that particular part of his training.

Obi Wan just looked at him, his face carefully blank. When Anakin slowly obeyed, kneeling down in front of him, Obi Wan moved to stand next to the young man. He took a deep breath, and as he settled into his own meditation, his fingertips slid over Anakin's shoulder, a small sign of affection, which he knew Anakin wasn't ready to accept right now, but would need shortly enough.

It took a while for both of them to find the inner calm, letting the mind float in the Force.
But, finally, peace descended on troubled minds. Obi Wan took his time coming back out. He didn't like the next part, but he saw no way around it. Anakin was getting strong in the Force. Very strong. He couldn't be allowed these outbursts of disrespect and agitation. He needed to learn the discipline needed to keep himself grounded in the ways of the Jedis.
Obi Wan sighed softly. This wasn't their first rodeo, but he certainly hoped it would be their last. Although he very much doubted that.

"Well, Anakin?" He said, moving to stand in front of his padawan.
Anakin opened his eyes, looking up at Obi Wan, keeping respectful eye-contact as he replied: "I apologize, Master. I was discourteous and insubordinate."
"Anakin, you must be more patient. Think."
"Yes, Master"
"You must stop these outbursts. Control your feelings, Padawan, or they will lead you astray."
"I am deeply sorry, Master. And I will accept your teachings."

Obi Wan looked away from the upturned face. Anakin said the words, but did he mean them? He sounded sincere, like he did every time he apologized, but the flame of rebellion burned as strong as ever behind the submissive tone and attitude.

"Very, well, then. You know the next part. Strip and stand to me."
As Anakin found his feet, discreetly shaking his legs a little, sore after having knelt on the hard floor for so long, Obi Wan briskly walked to his desk and pulled out a leather strap.
It was a brown, subtle thing, about 3 fingers wide and 2 feet long. He shook it out, then shook his head. He'd have to remember to oil it soon. After all it was something of a heirloom, having been passed down to him from Qui Gon, who, as they were packing up just before their last mission together, had handed it over, jokingly saying that he knew from experience, that using such a tool correctly was easier if you were familiar with it and knew exactly how it felt to be on the other end of it, and that since Obi Wan was getting beyond being on the receiving end, he could have it for any future apprentices, he might choose to teach.

As Obi Wan strode back to his apprentice, Anakin turned his back and straightened into a parade-stand.
He'd stripped his tunics off his shoulders, his slim waist hugged by his belt along with the layers of linen fabrics bundled into the thick brown leather.
His naked back, with its planes of muscles, broadening under the exercise and down-right hard work of his life looked so white and vulnerable that Obi Wan had to grit his teeth to keep his determination firm.

"What's the rule, Anakin?"
"One stroke extra each time we end up here, Master."
"And how many would that be this time?"
Anakin sighed softly. "15, Master. I am sorry"
"I wish you would listen to me. I don't like doing this, you know."
"I am trying, Master."
"Well, try harder."
"Yes, Master."

Obi Wan lifted the strap behind his shoulder and landed the first stripe across the young man's shoulder-blades.
He didn't drag things out. He applied the strap in a steady rhythm, letting just enough time pass between each stroke for Anakin to have a chance to breathe, knowing from experience how the air tended to get pushed out of you each time the leather danced across your back.

Anakin hissed when the first stroke landed, but didn't move. The next handful was met with stoical silence, but no one would have been able to keep that up, and neither could the Chosen One. Soft grunts became gasps and the strong young body rocked with each resounding slap.

The strap didn't break the skin. It could be wielded harshly, pounding muscles, bruising skin, but Obi Wan would never do that, like Qui Gon never had. He held back the force of the blows enough to ensure that the skin at his target was reddened to a brightly hot hue and sorely stinging, but never damaged.

That didn't mean the pain wasn't enough to break through the hardest of padawan heads. Both Qui Gon and Obi Wan himself had had a rebellious streak a mile wide in their youths. He really hoped the old strap would have the same effect on Anakin, as it had had on his predecessors.

During the last couple of strokes, Anakin started shifting his weight from foot to foot, his breathing hitching unsteadily.
When Obi Wan let the strap find it's target for the last time, slamming it a little harder onto skin already red and sore from earlier encounters, Anakin gave a soft cry.
Finally he heard the strap land on the floor, and at the cue of that sound, he folded down to a squat, hugging himself, going "Ow, Ow, Ow" under his breath.

Obi Wan waited patiently for the kid to find his balance. When Anakin finally stood up and turned to face his master, he was met with a gentle smile.
Anakin straightened with a grimace.
"Thank you, My Master," he said solemnly.
Obi Wan shook his head, "Please, don't make me do that again."
"I'll try, Master."
"Good. We have to go guard the Senator's rooms soon. I'll go to the main room now. That will give you an hour to rest a bit, before going to your station outside her bedroom door when she turns in. Meet me there."
"Yes, Master."
"Good now turn around and roll your shoulders for me."
Anakin obeyed, wincing, but Obi Wan was relieved to see that the strapping hadn't done any more damage than making the skin across the shoulder blades red as fire– the boy's movements would be unrestricted should the need to fight arise.
He reached out and ruffled the younger man's hair. "You'll do, go rest."
Anakin flashed him a subdued grin, and went into his bedroom, walking carefully.