Where can I find the original Arabic text of this narration by Ibn Mas'ud?

I need the original Arabic text of the following narration:- Ibn Mas'ud used to say, "When you bless the Prophet, then make the prayer on him excellent. You do not know; perhaps it will be shown to him. Say, ‘O Allah, bestow your mercy and your blessing on the Master of the Messengers, the Imam of the God-fearing, the Leader of the Good and the Messenger of Mercy.’"