I said: "O Messenger of Allah! Inform me about a matter that I may hold fast to." He said: 'Say: My Lord is Allah, then be steadfast.' I said: "O Messenger of Allah! What do you fear most for me?" So he took hold of his tongue and said: 'This.'"
Jami` at-Tirmidhi Book 36, Hadith 108
← Previous Hadith "For whomever Allah protects against the evil of what is between his jaws and the evil of what is between his legs, he shall enter Paradise."

Jami` at-Tirmidhi Book 36, Hadith 107 Next Hadith → "Do not talk too much without remembrance of Allah. Indeed excessive talking without remembrance of Allah hardens the heart. And indeed the furthest of people from Allah is the harsh-hearted."

Jami` at-Tirmidhi Book 36, Hadith 109