Surah 19. Maryam, Ayah 28

In ancient Semitic usage, a person's name was often linked with that of a renowned ancestor or founder of the tribal line. Thus, for instance, a man of the tribe of Banu Tamim was sometimes addressed as "son of Tamim" or "brother of Tamim". Since Mary belonged to the priestly caste, and hence descended from Aaron, the brother of Moses, she was called a "sister of Aaron" (in the same way as her cousin Elisabeth. the wife of Zachariah, is spoken of in Luke i, 5, as one "of the daughters of Aaron").

 i.e., his twin in virtue. They meant that they did not expect her to do something like that because they held her in high esteem like Aaron, Moses’ brother (perhaps because she was his descendant).

Aaron the brother of Moses was the first in the line of Israelite priesthood. Mary and her cousin Elisabeth (mother of Yahya) came of a priestly family, and were therefore, "sisters of Aaron" or daughters of 'Imran (who was Aaron's father). See n. 375 to iii. 35. Mary is reminded of her high lineage and the unexceptionable morals of her father and mother. How, they said, she had fallen, and disgraced the name of her progenitors!