Muhammad bin Muslim bin Khabbab said: Anas bin Malik (may Allah be pleased with him) came and sat in this place of yours, and said: "Do you know what this piece of wood is?" We said: No. He said: When the Prophet (peace and blessings be upon him) stood for prayer, he would take it in his right hand and say: "Straighten up, make your rows straight." Then he would take it in his left hand and say: "Straighten up, make your rows straight." When the mosque was demolished, the piece of wood went missing. Umar (may Allah be pleased with him) searched for it and found that Banu Amr bin Awf had taken it and placed it in their mosque, so he took it and returned it.
Umm Qays bint Mihsan (may Allah be pleased with her) relates that when the Messenger of Allah (peace and blessings be upon him) grew heavy (in old age), he set up a pillar at his place of prayer and would lean on it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5352