Steadfastness

On the authority of Abu ʿAmr, and he is also called Abu ʿAmrah, 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."

Related by Muslim.