For thou, O my God, hast told thy servant that thou wilt build him an house: therefore thy servant hath found in his heart to pray before thee. (1 Chronicles 17:25)
If God had not Himself promised to establish David’s name and throne forever, David’s prayer would have been bold, presumptuous, and arrogant. The king’s prayer was an expression, not of his own will, but of God’s. Thus he was only praying that God’s will be done.