Riyad as-Salihin, Book 1, Hadith 146 (In-Book) ⓘ

Anas (May Allah be pleased with him) reported: The Prophet came into the mosque and noticed a rope stretched between two poles. He enquired, "What is this rope for?" He was told: "This is Zainab's rope. When during her voluntary prayer, she begins to feel tired, she grasps it for support". The Prophet said, "Untie it. You should perform prayers so long as you feel active. When you feel tired, you should go to sleep".[Al-Bukhari and Muslim].

وعن أنس رضي الله عنه قال‏:‏ دخل النبي صلى الله عليه وسلم المسجد فإذا حبل ممدود بين الساريتين فقال‏:‏ ‏"‏ما هذا الحبل‏"‏ قالوا ‏:‏ هذا حبل لزينب، فإذا فترت تعلقت به‏.‏ فقال النبي صلى الله عليه وسلم ‏"‏ حلوه، ليصل أحدكم نشاطه فإذا فتر فليرقد‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏ ‏.‏