Sayyiduna Anas (may Allah be pleased with him) says: I have performed prayer with the Messenger of Allah (peace and blessings be upon him), Sayyiduna Abu Bakr as-Siddiq (may Allah be pleased with him), Sayyiduna Umar al-Faruq (may Allah be pleased with him), and Sayyiduna Uthman (may Allah be pleased with him), but I did not hear any one of them recite "Bismillah ir-Rahman ir-Rahim" aloud in the prayer.