John Gill Commentary 1 Kings 8:26

"Now therefore, O God of Israel, let thy word, I pray thee, be verified, which thou spakest unto thy servant David my father." — 1 Kings 8:26 (ASV)

And now, O God of Israel, let your word, I pray you, be verified: Truly made good, and punctually performed.

which you spoke to your servant David my father: the same request in other words, repeated to show his ardent and vehement desire to have it fulfilled.