Musnad Ahmad 32:1746

'Affan narrated to us, Hammad narrated to us, he said: Thabit informed us, from 'Abd al-Rahman ibn Abi Layla, that the Messenger of Allah (may Allah bless him and grant him peace) saw a rope in the mosque between two pillars. He said: "What is this rope?" It was said: "O Messenger of Allah, it belongs to Hamnah bint Jahsh; she prays, and when she becomes exhausted, she hangs onto it." The Messenger of Allah (may Allah bless him and grant him peace) said: "Let her pray as long as she is able, and when she becomes exhausted, let her sit."