The 21st of the 42 hadiths gathered by Imam Yahya ibn Sharaf an-Nawawi in An-Nawawi's Forty Hadith, given below in the original Arabic with an English translation and its reference.
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]
Sunni collections: text from the open hadith-api dataset. Al-Kafi: Arabic text, Muhammad Sarwar's translation and gradings from Thaqalayn.net via the Thaqalayn API. Hadith numbering follows those editions and can differ from a printed copy — check the Arabic against a trusted edition before relying on a reference.
