Sunan Ibn Majah 3972

Sufyan bin ‘Abdullah Thaqafi said:“I said: ‘O Messenger of Allah, tell me of something that I can adhere to.’ He said: ‘Say: “Allah is my Lord,” then stand straight (adhere steadfastly to Islam).’ He said: ‘O Messenger of Allah, what is the thing that you fear most for me?’ The Messenger of Allah (ﷺ) took hold of his own tongue, then he said: ‘This.’”