The Messenger of Allah ﷺ passed by Saad while he was supplicating with two fingers, and he said, "Use one, Saad."
حدثنا وكيع عن سفيان عمن
مر رسول الله ﷺ بسعد وهو يدعو بأصبعين فقال أحد يا سعد
Its chain of transmission is daif, containing an unknown narrator, and the hadith has already appeared at 9402 and 10687.