Abdullah bin Abbas (may Allah be pleased with them both) narrates: Once the Prophet Muhammad (peace be upon him) slept while he was in the state of prostration, to the extent that he began to snore. Then he stood up and performed prayer. I said: "O Messenger of Allah! You had slept." The Prophet (peace be upon him) replied: "Ablution is obligatory upon the one who sleeps lying down, because when he sleeps lying down, his joints become loose." In narrating this report from Abu Qatadah, Abu Khalid is alone; this narration is not reliable.

Sayyiduna Muawiyah bin Abu Sufyan (may Allah be pleased with him) narrates: The Noble Prophet (peace and blessings be upon him) said: "The eye is the restraint of the anus, so when the eye sleeps, this restraint is broken."

This narration is also transmitted with another chain of transmission.

Sayyiduna Amr bin Shu'aib narrates from his father, from his grandfather: The Noble Prophet (peace and blessings be upon him) said: "Whoever falls asleep while sitting, wudu is not obligatory upon him; but whoever lies down on his side (on the ground), wudu will be obligatory upon him."

Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) narrates: The Noble Prophet (peace and blessings be upon him) said: "The eye is the fastener of the anus; whoever sleeps should perform ablution well."