A.T. Robertson Commentary Galatians 4:23

"Howbeit the [son] by the handmaid is born after the flesh; but the [son] by the freewoman [is born] through promise." — Galatians 4:23 (ASV)

Is born (γεγεννητα). Perfect passive indicative of γενναω, stand on record so.

Through promise (δι' επαγγελιας). In addition to being "after the flesh" (κατα σαρκα).