Sunan an-Nasa'i 1643
It was narrated from Anas bin Malik that:
The Messenger of Allah (ﷺ) entered the masjid and saw a rope tied between two pillars. He said: "What is this?" They said: "It is for Zainab when she prays; if she gets tired she holds on to it." The Prophet (ﷺ) said: "Untie it. Let any one of you pray as long as he has energy, and if he gets tired let him sit down."
أَخْبَرَنَا عِمْرَانُ بْنُ مُوسَى، عَنْ عَبْدِ الْوَارِثِ، قَالَ حَدَّثَنَا عَبْدُ الْعَزِيزِ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم دَخَلَ الْمَسْجِدَ فَرَأَى حَبْلاً مَمْدُودًا بَيْنَ سَارِيَتَيْنِ فَقَالَ ‏"‏ مَا هَذَا الْحَبْلُ ‏"‏ ‏.‏ فَقَالُوا لِزَيْنَبَ تُصَلِّي فَإِذَا فَتَرَتْ تَعَلَّقَتْ بِهِ ‏.‏ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ حُلُّوهُ لِيُصَلِّ أَحَدُكُمْ نَشَاطَهُ فَإِذَا فَتَرَ فَلْيَقْعُدْ ‏"‏ ‏.‏