Sayyiduna Anas (may Allah be pleased with him) narrates that I have offered prayers behind the Prophet (peace and blessings of Allah be upon him), Sayyiduna Abu Bakr, Umar, and Uthman (may Allah be pleased with them), and they did not recite « بِسْمِ اللهِ الرَّحْمٰنِ الرَّحِيْمِ » aloud.