Ibn Hibban

Mus'ab bin Thabit narrates: I came and sat down, then Muhammad bin Muslim informed: Sayyiduna Anas bin Malik (may Allah be pleased with him) arrived and sat down in your place. He said: Do you people know what this piece of wood is? We replied: No. He informed: When the Prophet (peace and blessings be upon him) would stand for prayer, he would hold it with his blessed hand, then he would turn and say: Maintain straightness and correct your rows. Then he would hold it in his left hand and say: Maintain straightness and correct your rows. Then, when the mosque was demolished, this piece of wood was lost. Sayyiduna Umar (may Allah be pleased with him) searched for it, and he found this piece of wood. This piece of wood had been taken by Banu Amr bin Awf and they had placed it in their mosque. Sayyiduna Umar brought it back from there and placed it in its (previous specific) place.