Surah 15. Al-Hijr, Ayah 52

For the reason of Abraham's and Sarah's apprehension, see 11:70 .

 As mentioned in 11:69-70, the angels came to Abraham in the form of men and when he offered them food, they did not eat. In ancient Middle Eastern culture, if a guest refused to eat the food provided by their host, it was a sign of ill-will.

For a full understanding of this reference to the angels who were Abraham's guests and came to announce the birth of a son to him in his old age, read xi. 69-73 and notes. The appearance of two strangers of uncommon appearance, who refused to partake of the host's sumptuous hospitality, made Abraham at first suspicious and afraid.