Compiled by Imam Yahya ibn Sharaf al-Nawawi
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.
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].