فَأَوْجَسَ مِنْهُمْ خِيفَةً ۖ قَالُوا لَا تَخَفْ ۖ وَبَشَّرُوهُ بِغُلَامٍ عَلِيمٍ (28)
(51:28) Then he became afraid of them. *26 They said: 'Fear not,' and announced to him the good news of (the birth of) a boy endowed with knowledge. *27
*26) That is, "When they did not stretch out their hands for food, the Prophet Abraham became afraid in his heart. The reason for this fear could be that in tribal life the strangers' going to a house and avoiding food used to be an indication that they had come with an evil design. But most probably when they. refrained from food the Prophet Abraham realized that they were angels, who had come in human guise; and since the angels came in human guise only on extraordinary occasions, he became afraid that they must have come in that guise on some dreadful mission.
*27) According to Surah Hud: 71, this was the good news of the birth of the Prophet Isaac (peace be upon him) and this also contained the good news that through the Prophet Isaac he would have a grandson like the Prophet Jacob (peace be upon him).