Asam bin Qdamh al-Bjly عصام بن قدامة البجلي · The Book of Forgetfulness (In Prayer)

When the Messenger of Allah (ﷺ) sat during the prayer, he put his hands on his knees and raised the finger that is next to the thumb, and supplicates with it, and his left hand was on his knee laid on it.

A man used to supplicate with two fingers and the Messenger of Allah (ﷺ) said: "Make it one, make it one."