Verses with the word solemnly in the Old Testament (2 verses):

Genesis 43:3
And Judah spake unto him, saying, The man did solemnly protest unto us, saying, Ye shall not see my face, except your brother be with you.

1 Samuel 8:9
Now therefore hearken unto their voice: howbeit yet protest solemnly unto them, and shew them the manner of the king that shall reign over them.