Finding songs about slavery that were sung at the time is difficult. Most such songs were recorded after slavery ended and can only be attributed to that time. They have been remade through the folk process or are post-slavery. Here is one, a work song (rowing) with music, that was recorded pre-Civil War, published in 1859 in a work about plantation life of the 1830s.
Compare with "Mother, Is Massa Gwine to Sell Us?" which probably is a post-slavery revision of a secular song with religious material added (in this thread, 21 Dec 01, Dicho).
Dena Epstein (reference below) notes "sacred texts gradually replaced secular texts in boat songs as the century progressed. By the time Northerners arrived in the Sea Islands in 1862, most of the songs were sacred. Many of the northerners were unaware of a tradition of secular music among the blacks and sincerely believed that they sang only hymns, relegating all frivolous and worldly music to the minstrel theatre."   

SOLD OFF TO GEORGY

Farewell, fellow servants! O-ho! O-ho!
I'm gwine away to leabe you; O-ho! O-ho!
I'm gwine to leabe de ole county; O-ho! O-ho!
I'm sold off to Georgy! 0-ho! O-ho!

Farewell, ole plantation, O-ho! O-ho!
Farewell, de ole quarter, O-ho! O-ho!
Un daddy, un mammy, O-ho! O-ho!
Un marster, un missus! O-ho! O-ho!

My dear wife un one chile, O-ho! O-ho!
My poor heart is breaking; O-ho! O-ho!
No more shall I see you, O-ho! O-ho!
Oh! No more for-eber! O-ho! O-ho!

James Hungerford, 1859, "The Old Plantation, and What Is Gathered There in an Autumn Month." Harper & Bros., NY. (Note: discusses Juba(h) dance and boat songs, two with music). Song and reference from Dena J. Epstein, 1977, "Sinful Tunes and Spirituals." Worksongs, p. 170-171.
Art Thieme, in this thread, posted another song from Epstein's excellent, authoritative reference; by far the best for music of the slavery period.