Musnad Ahmad 26:722

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Sulayman, from Ibrahim, that al-Aswad and ‘Alqamah were with ‘Abdullah in the house. ‘Abdullah said: "Have these people prayed?" They said: "Yes." He said: "So he prayed with them without an Adhan or an Iqamah, and he stood in their midst. He said: 'If you are three, do like this. If you are more, let one of you lead you in prayer, and let one of you place his hands between his thighs when he bows, and let him bend forward.' It is as if I am looking at the interlacing of the fingers of the Messenger of Allah, may Allah bless him and grant him peace."