Anas (May Allah be pleased with him) reported:
The Prophet (ﷺ) 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 (ﷺ) 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].
Arabic/English book reference: Book 1, Hadith 146