«مَا الَّذِي أَحَالَ صِفَتَكَ حَتَّى جَهِلْتُ مَعْرِفَتَكَ؟»
What changed your appearance so much that I failed to recognize you?
Aḥāla means to alter or transform in this context; ṣifah refers to outward condition, and maʿrifah to recognition or knowledge of a person.
The narrator voices the puzzle directly. His next question narrows the matter to the whitening of the beard. The exchange distinguishes a person’s enduring identity from the appearance that can change with age and experience.