From the book Al-Minhatu Ar-Rabbaaniyah Fee Sharh Al-Arba'een An-Nawawiyah by Shaikh Saalih Al-Fawzaan.
Today we begin the explanation of Hadith 21:
On the authority of Aboo 'Amr - and he is also called Aboo 'Amrah - Sufyaan bin Abdillaah ath-Thaqafee (radiAllaahu anhu) who said :
I said : "O Messenger of Allaah, tell me something about al-Islaam which I can ask of no one but you."
He said : "Say: I believe in Allaah - and then be Steadfast"
It was related by Muslim.