Surah Maryam — Ayah 17 (19:17)
فَٱتَّخَذَتۡ مِن دُونِهِمۡ حِجَابٗا فَأَرۡسَلۡنَآ إِلَيۡهَا رُوحَنَا فَتَمَثَّلَ لَهَا بَشَرٗا سَوِيّٗا ١٧
English translation (Saheeh International)
And she took, in seclusion from them, a screen. Then We sent to her Our Angel [i.e., Gabriel], and he represented himself to her as a well-proportioned man.
Brief commentary
Thus, she made for herself a veil from the people which would cover her, so that they cannot see her when she is worshipping her Lord. Then I sent Gabriel (peace be upon him) to her, thus he appeared to her in the form of a perfectly-formed human. So she thought he has a malicious intention towards her.