He asked for forgiveness two times, and the third time he did not…Why?!

Ibn Kathir wrote in al-Bedayah wal-Nihayah (The Beginning and the End) that once a servant of Abdullah ibn Omar made a mistake for which he deserved to be punished. He was brought before Abdullah to be questioned. Abdullah asked the man why he made such a mistake. The man asked Abdullah “Have you never sinned’?” Abdullah replied: “Yes, I have many times.” The man said “And Allah forgave you. So be kind to me as Allah has been kind to you.” Abdullah immediately forgave the man. The servant made the same mistake a second time, and Ibn Omar wanted to punish him, so the servant said the same, and Ibn Omar did not punish him. He made the same mistake for the third time, and Ibn Omar punished him this time but the servant did not talk. Ibn Omar asked him: Why did not you say what you said the last couple of times? He replied: O Sir, because I feel ashamed of your patience while I repeat my mistakes. Ibn Omar cried and said: I should be the one ashamed before my Lord. You are free for the sake of Almighty Allah.

Refer to: al-Bedayah wal-Nihayah (The Beginning and the End) (13/205)