Alqamah and al-Aswad (may Allah have mercy on them both) narrate: We prayed with Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him); when he bowed, he pressed his two palms together and placed them between his knees, and he struck our hands (to teach us this), so we did the same.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9284