Verses with the word doubtless in the Old Testament (4 verses):

Numbers 14:30
Doubtless ye shall not come into the land, concerning which I sware to make you dwell therein, save Caleb the son of Jephunneh, and Joshua the son of Nun.

2 Samuel 5:19
And David enquired of the LORD, saying, Shall I go up to the Philistines? wilt thou deliver them into mine hand? And the LORD said unto David, Go up: for I will doubtless deliver the Philistines into thine hand.

Psalms 126:6
He that goeth forth and weepeth, bearing precious seed, shall doubtless come again with rejoicing, bringing his sheaves with him.

Isaiah 63:16
Doubtless thou art our father, though Abraham be ignorant of us, and Israel acknowledge us not: thou, O LORD, art our father, our redeemer; thy name is from everlasting.