It was narrated from Anas bin Malik that the Messenger of Allah entered the Masjid and saw a rope tied between two pillars. He said, "What is this rope?" They said: "It belongs to Zainab. She prays here and when she gets tired she holds on to it." He said: "Untie it, untie it, and let any one of you pray when he has energy, and if he gets tired let him sit down." (Sahih)