'Sincerely' in the Bible

Solomon replied, "You demonstrated great loyalty to your servant, my father David, as he served you faithfully, properly, and sincerely. You have maintained this great loyalty to this day by allowing his son to sit on his throne.

My words come from the uprightness of my heart, and my lips will utter knowledge sincerely.

A prayer of David. Lord, consider my just cause! Pay attention to my cry for help! Listen to the prayer I sincerely offer!

The Lord is near all who cry out to him, all who cry out to him sincerely.