Musnad Ahmad 32:320

Abu al-Muthanna Mu'adh ibn Mu'adh al-'Anbari narrated to us, he said: Hammad ibn Salamah narrated to us, Thabit al-Bunani narrated to us, from Anas ibn Malik, from the Prophet, peace and blessings of Allah be upon him, regarding the saying of Allah the Exalted: {And when his Lord appeared to the mountain} [Al-A'raf: 143]. He said: "He said: 'Like this,' meaning that He brought out the tip of the little finger." My father said: "Mu'adh showed it to us." He said: Humayd al-Tawil said to him: "What do you intend by this, O Abu Muhammad?" He said: So he struck his chest a severe strike and said: "Who are you, O Humayd? And what are you, O Humayd? Anas ibn Malik narrates it to me from the Prophet, peace and blessings of Allah be upon him, and you say: 'What do you intend by it?'"