Whenever the Messenger of Allah ﷺ sat during the prayer, he would place his hands upon his knees and raise the finger next to his thumb, supplicating with it, while his left hand rested on his other knee, spread out upon it.
أخبرنا محمد بن رافع قال حدثنا عبد الرزاق قال أنبأنا معمر عن عبيد الله عن نافع
أن رسول الله ﷺ كان إذا جلس في الصلاة وضع يديه على ركبتيه ورفع أصبعه التي تلي الإبهام فدعا بها ويده اليسرى على ركبته باسطها عليها
[sahih] Extracted by Muslim, in the Book of Mosques, chapter on the manner of sitting in prayer and how to place the hands on the thighs, no. 580, from Muhammad bin Rafi with the same wording. It is also found in Kubra, no. 1192.