It is narrated from Sayyiduna Shaddad bin Shurahbil al-Ansari (may Allah be pleased with him); he said: Whatever I may forget, I have not forgotten that I saw the Messenger of Allah (peace and blessings be upon him) standing in prayer, with his (peace and blessings be upon him) right hand over his left hand, holding it.
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7080