Sahih Muslim Book - 25, Hadith - 4231

وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى وَأَبُو بَكْرِ بْنُ أَبِى شَيْبَةَ - وَاللَّفْظُ لِيَحْيَى - قَالَ أَخْبَرَنَا إِسْمَاعِيلُ ابْنُ عُلَيَّةَ عَنِ ابْنِ عَوْنٍ عَنْ إِبْرَاهِيمَ عَنِ الأَسْوَدِ بْنِ يَزِيدَ قَالَ ذَكَرُوا عِنْدَ عَائِشَةَ أَنَّ عَلِيًّا كَانَ وَصِيًّا فَقَالَتْ مَتَى أَوْصَى إِلَيْهِ فَقَدْ كُنْتُ مُسْنِدَتَهُ إِلَى صَدْرِى - أَوْ قَالَتْ حَجْرِى - فَدَعَا بِالطَّسْتِ فَلَقَدِ انْخَنَثَ فِى حَجْرِى وَمَا شَعَرْتُ أَنَّهُ مَاتَ فَمَتَى أَوْصَى إِلَيْهِ؟

It was narrated that Al-Aswad bin Yazid said: "They said in the presence of 'Aishah that 'Ali was bequeathed something by the Prophet (s.a.w). She said: 'When did he make a will for him? He was leaning on my chest' - or she said: 'in my lap - and he called for a bowl, then he fell into my lap and I did not realize that he had died. So when did he make a will for him?"'