(a) Qabisah bin Hulb narrates from his father (may Allah be pleased with him) that he said: I saw the Messenger of Allah (peace and blessings be upon him) in the prayer with his right hand placed on his left hand.
(b) Hulb's name is Yazid bin Qunafah. It is transmitted from al-Harith bin Ghudayf al-Kindi and Shaddad bin Shurahbil al-Ansari (may Allah be pleased with them both) that they saw the Prophet (peace and blessings be upon him) doing this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2328