Genesis 17:17

17:17 Then Abraham bowed down with his face to the ground and laughed40 as he said to himself,41 “Can42 a son be born to a man who is a hundred years old?43 Can Sarah44 bear a child at the age of ninety?”45

40	sn Laughed. The Hebrew verb used here provides the basis for the naming of Isaac: “And he laughed” is וַיִּצְחָק (vayyitskhaq); the name “Isaac” is יִצְחָק (yitskhaq), “he laughs.” Abraham’s (and Sarah’s, see 18:12) laughter signals disbelief, but when the boy is born, the laughter signals surprise and joy.
41	tn Heb “And he fell on his face and laughed and said in his heart.”
42	tn The imperfect verbal form here carries a potential nuance, as it expresses the disbelief of Abraham.
43	tn Heb “to the son of a hundred years.”
44	sn It is important to note that even though Abraham staggers at the announcement of the birth of a son, finding it almost too incredible, he nonetheless calls his wife Sarah, the new name given to remind him of the promise of God (v. 15).
45	tn Heb “the daughter of ninety years.”