This text comes from Poems on Slavery, a historical songbook transcribed on Wikisource and reproduced from the pinned revision linked below.
Loud he sang the psalm of David!
He, a Negro and enslaved,
Sang of Israel's victory,
Sang of Zion, bright and free.
In that hour, when night is calmest,
Sang he from the Hebrew Psalmist,
In a voice so sweet and clear
That I could not choose but hear,
Songs of triumph, and ascriptions,
Such as reached the swart Egyptians,
When upon the Red Sea coast
Perished Pharaoh and his host.
And the voice of his devotion
Filled my soul with strange emotion;
For its tones by turns were glad,
Sweetly solemn, wildly sad.
Paul and Silas, in their prison,
Sang of Christ, the Lord arisen,
And an earthquake's arm of might
Broke their dungeon-gates at night.
But, alas! what holy angel
Brings the Slave this glad evangel?
And what earthquake's arm of might
Breaks his dungeon-gates at night?