Musnad Ahmad 32:1344

Rawh narrated to us, Sa'id narrated to us, from Qatadah, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) used to raise his middle finger and the one next to it, then say: "I and the Hour have been sent like these two." And he did not prefer one of them over the other.