The promise of righteous offspring

فَأَوْجَسَ مِنْهُمْ خِيفَةً ۖ قَالُوا۟ لَا تَخَفْ ۖ وَبَشَّرُوهُ بِغُلَـٰمٍ عَلِيمٍ

And he felt from them apprehension. They said, "Fear not," and gave him good tidings of a learned boy.