Narrated Ibn `Abbas:
'Allah is Sufficient for us and He Is the Best Disposer of affairs," was said by Abraham when he was thrown into the fire; and it was said by Muhammad when they (i.e. hypocrites) said, "A great army is gathering against you, therefore, fear them," but it only increased their faith and they said: "Allah is Sufficient for us, and He is the Best Disposer (of affairs, for us)." (3.173)
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 86
Arabic reference: Book 65, Hadith 4563