3. [3/96] al-Tahdhib: By the chain to al-Husayn b. Sa`id from Hammad from Hariz from Zurara who said:

I said to him: a man in Wudhu falls asleep – closing his eyes for a beat or two – does this mean that he is obliged to renew Wudhu? he said: O Zurara, the eye may sleep while the heart and the ear are awake, only when the eye, the ear and the heart all sleep does Wudhu become obligatory, I said: what if something moves near him while he is not even aware of it, he said: no [that does not mean he has to renew Wudhu], unless he is certain that he has fallen asleep and unless there manifests a clear sign indicating that, if not then he was certain about his initial Wudhu and certainty is never overriden by doubt rather what overrides it [certainty] is another certainty [he become sure of a new event].