«سَتَجِدُ مَطْلَعِي عَلَيْكَ أَسْرَعَ مِنْ ارْتِدَادِ طَرْفِكَ إِلَيْكَ»
You will find me appearing before you sooner than your glance returns to you.
Maṭlaʿī here refers to his reappearance. Asraʿ min is a comparative construction, “faster than,” and ṭarf refers to the eye or its glance.
The promise is obvious hyperbole. It sounds confident, but the relevant evidence will not be the beauty of its wording; it will be whether the speaker actually returns.