Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) entered the mosque, and there was a rope hanging between two pillars. He (peace be upon him) asked: What is the reason for this? The companions said: This belongs to Sayyida Zainab (may Allah be pleased with her); when she becomes tired, she hangs onto it. He (peace be upon him) said: Untie it; a person should pray in a state of activity and alertness. When he becomes tired, he should leave standing (in prayer). In another narration, it is stated: He should pray as long as he understands (what he is reciting), and when he becomes overpowered (by sleep), he should go to sleep.