Forty Hadith An-Nawawi

On the authority of Abu `Amr — and he is also called Abu `Amrah — Sufyan bin Abdullah ath- Thaqafee (may Allah be pleased with him) who said: I said, ""O Messenger of Allah, tell me something about al-Islam which I can ask of no one but you."" He (peace and blessings of Allah be upon him) said, ""Say I believe in Allah — and then be steadfast."" [Muslim]