Riyad as-Salihin 1517
Sufyan bin 'Abdullah (May Allah be pleased with him) reported:
I asked: "O Messenger of Allah! Tell me, of something to which I may remain steadfast." He (ﷺ) said, "Say: My Rubb is Allah and then remain steadfast." Then I said: "O Messenger of Allah! What do you fear most about me?" He took hold of his own tongue and said: "This." [At-Tirmidhi] .
وعن سفيان بن عبد الله رضي الله عنه قال‏:‏ قلت يا رسول الله حدثني بأمر أعتصم به قال‏:‏ ‏
"‏ قل ربي الله ثم استقم‏"‏ قلت‏:‏ يا رسول الله ما أخوف ما تخاف علي‏؟‏ فأخذ بلسان نفسه، ثم قال‏:‏ “هذا”‏.‏ رواه الترمذي وقال حديث حسن صحيح‏.‏