Sunan Ibn Majah Book 6, Hadith 1626

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا إِسْمَاعِيلُ ابْنُ عُلَيَّةَ، عَنِ ابْنِ عَوْنٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، قَالَ: ذَكَرُوا عِنْدَ عَائِشَةَ أَنَّ عَلِيًّا كَانَ وَصِيًّا ‏.‏ فَقَالَتْ: مَتَى أَوْصَى إِلَيْهِ؟ فَلَقَدْ كُنْتُ مُسْنِدَتَهُ إِلَى صَدْرِي - أَوْ إِلَى حِجْرِي فَدَعَا بِطَسْتٍ فَلَقَدِ انْخَنَثَ فِي حِجْرِي فَمَاتَ وَمَا شَعَرْتُ بِهِ. فَمَتَى أَوْصَى ـ صلى الله عليه وسلم ـ؟ ‏

It was narrated that Aswad said:“They said in ‘Aishah’s presence that ‘Ali was appointed (by the Prophet (ﷺ) before he died), and she said: ‘When was he appointed? He (the Prophet (ﷺ)) was resting against my bosom, or in my lap, and he called for a basin, then he became limp in my lap and died, and I did not realize it. So when did he (ﷺ) appoint him?’”