Sayyiduna Anas (may Allah be pleased with him) narrates: I have seen the companions (may Allah be pleased with them) of the Noble Prophet (peace and blessings be upon him); they would be made to stand for prayer, to the extent that sometimes I would even hear some of them snoring, but then they would get up and perform the prayer and would not perform ablution again. The narrator named Ibn Mubarak stated this: "According to us, this ruling is when they would fall asleep while sitting." This hadith is authentic.
Hadith Referenceسنن الدارقطني / كتاب الطهارة / 474
Hadith Takhrij«أخرجه مسلم فى ((صحيحه)) برقم: 376، وأبو داود فى ((سننه)) برقم: 200، والترمذي فى ((جامعه)) برقم: 78، والبيهقي فى((سننه الكبير)) برقم: 595، 596، 597، والدارقطني فى ((سننه)) برقم: 473، 474، 475، وأحمد فى ((مسنده)) برقم: 14154»