מלכים א ב:ל פירוש: רש״י

And he said, “No.” Two [punishments] I will not accept upon myself. The curses that your father Dovid cursed me at the death of Avner, as it is stated, “They shall fall upon the head of Yo’av.”¹⁸II Shmuel 3:29. let Shlomo accept them upon himself, and afterward I will go.