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.