Musnad Abu Ya'la al-Mawsili 152:135

On the authority of al-A’mash, from Ibrahim, from Alqama and al-Aswad, from Abdullah, who said: "When one of you bows, let him spread his forearms upon his thighs and let him hunch his back." He said: "It is as if I am looking at the interlacing of the fingers of the Messenger of Allah (ﷺ)." He said: "Then he joined his palms together and showed them to them."