It is narrated from Sayyiduna Sufyan bin Abdullah Thaqafi (may Allah be pleased with him), he says: I said, "O Messenger of Allah! Tell me about such a deed related to Islam that I may hold fast to it and after you, I may not need to ask anyone about it." The Prophet (peace and blessings be upon him) said: "Say, 'My Lord is Allah,' and then remain steadfast upon it." I said, "O Messenger of Allah! What do you fear most for me?" In another narration: "From what should I guard myself?" The Prophet (peace and blessings be upon him) held his blessed tongue and said: "This."