Mukhtasar Bukhari

Narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him): (Once in the mosque) the Noble Prophet (peace and blessings of Allah be upon him) entered and (saw that) a rope was hanging between two pillars. The Prophet (peace be upon him) said: "What is this rope?" The people replied that this rope was hung by Umm al-Mu'mineen Zainab (may Allah be pleased with her); when she becomes tired while standing in prayer, she holds on to this rope. The Noble Prophet (peace be upon him) said: "No, this should not be done at all. Untie it. Each of you should pray as long as he feels energetic, and when he becomes tired, he should sit down."