Sayyiduna Hulb al-Ta'i (may Allah be pleased with him) said: I saw the Prophet (peace and blessings be upon him) stand up to pray, and I saw that he (peace and blessings be upon him) placed one hand upon the other, the right hand upon the left.
Hadith Referenceالمعجم الكبير للطبراني / باب الهاء / 18642