Musnad Ahmad 30:3041

Waki' narrated to us, 'Abd al-'Aziz ibn 'Abd Allah ibn Abi Salamah narrated to us, from 'Abd Allah ibn al-Fadl, from al-A'raj, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said in his Talbiyah: "Here I am, O God of Truth."