He was praying and placed his left hand over his right. The Prophet ﷺ saw him and placed his right hand over his left.
أنه كان يصلي فوضع يده اليسرى على اليمنى. فرآه النبي ﷺ، فوضع يده اليمنى على اليسرى.
Abu Dawud (755), Nasai (888), and Ibn Majah (811) all narrated it through the route of Hushaym bin Bashir, from Hajjaj bin Abu Zaynab, who said, I heard Abu Uthman narrating from Ibn Masud, who said, then he mentioned it.Nawawi said in Sharh Muhazzab (3/312), "Its isnad is sahih according to the criteria of Muslim." I say, it is as he said, except that Hajjaj bin Abu Zaynab, although he is among the narrators used by Muslim, has some weakness in him. The summary regarding him is that he is "truthful but makes mistakes."Ahmad (15090), Tabarani in Awsat (7853), and Daraqutni (1106) all narrated it through the route of Muhammad bin Hasan Wasiti, who said, Abu Yusuf Hajjaj, meaning Ibn Abu Zaynab, narrated to us from Abu Sufyan, from Jabir, who said, "The Messenger of Allah ﷺ passed by a man who was praying and had placed his left hand over his right, so he pulled it away and placed his right hand over his left."Daraqutni said in Ilal (5/339), "The statement of Hushaym is more sahih."