Richie is correct.
No. 57, Jubilee Songs. J. B. T. Marsh, The Story of the Jubilee Singers with Their Songs, Houghton Mifflin c. 1880.
Lyrics do not seem to be in the Permathread or in mudcat.

Lyr. Add: When Moses Smote the Water
Fisk Jubilee Singers

Chorus:
When Moses smote the water,
The children all passed over,
When Moses smote the water,
The sea gave away.
1
O children ain't you glad
You've left that sinful army?
O children ain't you glad
The sea gave away?
2
O Christians ain't you glad
You've left that sinful army?
O Christians ain't you glad
The sea gave away?
3
O brothers ain't you glad
You've left that sinful army?
O brothers ain't you glad
The sea gave away?

With musical score. Cited from Marsh and reference given by Richie.