Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: Once the Prophet Muhammad (peace be upon him) passed by a rope tied between two pillars in the mosque. He inquired: "What is this rope for?" The people replied: "So-and-so woman performs prayer, and when she fears sleep overcoming her, she holds onto it." The Prophet Muhammad (peace be upon him) said: "She should pray as long as she is alert, and when sleep overcomes her, she should go to sleep."