Dovid Hamelech’s Reward:
Regarding the reward for one who is shamed and does not respond, Sefer Shevet Mussar (Perek 20, Ois 27) writes: One should try to be from amongst those who are shamed and do not respond. Dovid Hamelech saw that Shimi ben Geira cursed him with a terrible curse, and Avishai wanted to harm Shimi, but Dovid said, “Leave Him, for Hashem bade him to curse.” Even though he threw stones and dirt at Dovid, he did not allow him to be harmed. The Medrash says that at that time, the Bais Din Shel Mailoh appointed Dovid to be one of the four on the Merkavah (Divine Chariot).
Dovid Hamelech’s words are also proof to the Peleh Yoetz’s statement that shame atones for sin, as Dovid ordered Shimi to be left alone so that the curses would atone for his transgression.