When there are three followers, the imam should step forward

Hazrat Abdur Rahman bin Aswad says that Hazrat Alqama and Hazrat Aswad sought permission to visit Hazrat Abdullah. They were granted permission. Hazrat Abdullah said to them that soon there will come rulers who will delay the prayers from their prescribed times; at such times, you should perform the prayers at their proper times. Then he stood up and prayed between the two of us. Then he said that I have seen the Messenger of Allah, peace and blessings be upon him, do likewise.

It is narrated similarly through another chain of transmission.

Hazrat Ibn Umar (may Allah be pleased with them both) narrates that when there are three people, one should step forward and two should stand behind.

Hazrat Nafi' narrates that when Hazrat Ibn Umar (may Allah be pleased with them) led two men in congregation, he would make them stand behind him.

Hazrat Hisham states that when Hazrat Urwah led two men in prayer, he would make them stand behind him.

Ibrahim says that when there are three people, then one of them should step forward.

Hazrat Aamir says that when there are three people besides the Imam, then one of them should step forward.

Hazrat Usman bin Aswad says that I and another man offered prayer with Hazrat Mujahid. He made one of us stand on his right and the other on his left, and said that three people should pray in this manner.

The father of Hazrat Ubaidullah narrates that I came to Hazrat Umar while he was offering the Zuhr prayer. I stood on his left side, so he made me stand on his right side. Meanwhile, Yarfa also joined us in prayer, so we both moved back and offered the prayer behind him.

Hazrat Saeed bin Musayyib and Hasan say that when there are three people, one of them should step forward and the other two should pray behind him.

The father of Hazrat Ubaidullah narrates that I came to Hazrat Umar while he was offering prayer. (I stood on his left side, so) he made me stand on his right side. Meanwhile, Yarfa also joined us in prayer, so we both moved back.

Hazrat Ali (may Allah be pleased with him) said that when there are three people, one of them should step forward.