Sunan an-Nasai 18368
In-book no 3632أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا أَزْهَرُ، قَالَ أَنْبَأَنَا ابْنُ عَوْنٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، عَنْ عَائِشَةَ، قَالَتْ يَقُولُونَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم أَوْصَى إِلَى عَلِيٍّ رضى الله عنه لَقَدْ دَعَا بِالطَّسْتِ لِيَبُولَ فِيهَا فَانْخَنَثَتْ نَفْسُهُ صلى الله عليه وسلم وَمَا أَشْعُرُ فَإِلَى مَنْ أَوْصَى
It was narrated that 'Aishah said: "They say that the Messenger of Allah made a will concerning 'Ali, may Allah be pleased with him. But he called for a vessel in which to urinate, then he went limp without me realizing it. So to whom did he leave a will?"