Ubaydullah bin Abdullah bin Utbah (may Allah have mercy on him) said: I went to Sayyidah Aishah (may Allah be pleased with her) and said: Will you not tell me the hadith about the illness of the Prophet (peace and blessings be upon him)? She said: Of course! The Messenger of Allah (peace and blessings be upon him) became heavy (with illness), and he (peace and blessings be upon him) said: "Have the people prayed?" We said: No, O Messenger of Allah; they are waiting for you. He (peace and blessings be upon him) said: "Put water for me in the basin." We put the water, and he (peace and blessings be upon him) took a ritual bath (ghusl). Then he (peace and blessings be upon him) tried to get up, but he fainted. Then he (peace and blessings be upon him) came to, and he asked: "Have the people prayed?" We said: No, O Messenger of Allah; they are waiting for you. He (peace and blessings be upon him) said: "Put water in the basin." We did so. He (peace and blessings be upon him) took a bath, then tried to get up, but he fainted. Then he came to, and he (peace and blessings be upon him) said: "Have the people prayed?" We said: No, they are waiting for you, O Messenger of Allah. He (peace and blessings be upon him) said: "Put water for me in the basin." We put water in the basin. He (peace and blessings be upon him) took a bath, then tried to get up, but he fainted. Then he came to, and he (peace and blessings be upon him) said: "Have the people prayed?" We said: No, they are waiting for you, O Messenger of Allah. Sayyidah Aishah (may Allah be pleased with her) said: The people in the mosque were bowed over (from drowsiness), waiting for the Messenger of Allah (peace and blessings be upon him) for the Isha prayer. So the Messenger of Allah (peace and blessings be upon him) sent word to Sayyiduna Abu Bakr (may Allah be pleased with him) that he should lead the people in prayer.
(b) The Messenger of Allah (peace and blessings be upon him) considered taking a bath after fainting to be recommended, though ablution is also sufficient.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 604