2 Chronicles 6:4. "And [Solomon] said "Blessed be the Lord, the God of Israel, who with his hand has fulfilled what he promised with his mouth to David my father..." 

God always keeps his promises, always.  He is the only person we can be absolutely certain will never say He will do something and not do it. God's word will never change, because God is unchanging. (See His Promises Are Unbreakable.)

Solomon is extolling how God kept his promise to David that David's son would build a temple for the Lord, a promise that was made and kept within one generation. Sometimes God's promises take a lot longer to be kept; that is because only God knows the perfect time for all things to happen. It is important to note, too, that Solomon did an awful lot of work in building the temple. God always keeps His promises, but we have to do our part, too.