Isaac born
Genesis 21:1–7; Romans 4:18–21; Hebrews 11:11–12
As God had promised, Sarah gave birth to Isaac when Abraham was 100 and she was 90.
Sarah conceived, and bore Abraham a son in his old age, at the set time of which God had spoken to him.
Genesis 21:2 (World English Bible)
Twenty-five years after God first promised Abram offspring, the son arrived. Sarah, who had laughed in disbelief, now laughed for joy: “God has made me laugh” (21:6). Paul says Abraham didn't weaken in faith, even though his body was already worn out (Romans 4:19).
Dating notes
Abraham was 100 (Genesis 21:5).