Genesis 28:22

and this stone, which I have set for a pillar, shall be God's house; and of all that Thou shalt give me I will surely give the tenth unto Thee. It was not a condition which Jacob here expressed, but a thankful acknowledgment of the divine assurance. By this vow Jacob accepted the promise of the Lord and declared what, in his estimation, was included in it. He had a definite event before his eyes, for the stone which at present served only as a reminder of the miraculous vision, would be replaced by a monument of the presence and dwelling of God with His people, and of the gifts of God which would come to him as a result of that promise he herewith dedicated the tenth part to the Lord in return. That is the proper form of trust in God, to accept His promises in simple faith, and to worship and serve Him in turn.