Musnad Ahmad 26:347

'Ali ibn 'Abdullah narrated to us, Hammad ibn Zayd narrated to us, from Aban ibn Taghlib, from Abu Ishaq, from 'Abd al-Rahman ibn Yazid, from 'Abdullah, that he mentioned the Prophet, peace and blessings of Allah be upon him, used to say: "At your service, O Allah, at your service. At your service, there is no partner for You, at your service. Indeed, all praise and grace belong to You."