It is narrated from Sayyiduna Wa'il bin Hujr (may Allah be pleased with him) that when the Prophet (peace and blessings be upon him) stood in the prayer, he would grasp his left hand with his right hand. (The narrator said:) And I saw Alqamah doing the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2324