וְאַבְרָהָ֖ם בֶּן־מְאַ֣ת שָׁנָ֑ה בְּהִוָּ֣לֶד ל֔וֹ אֵ֖ת יִצְחָ֥ק בְּנֽוֹ׃
And Abraham was a hundred years old, when his son Isaac was born unto him.
Read Kabbalistic (mystical) interpretations of Genesis 21:5: Zohar and classical Jewish mystical sources, free online.