This text comes from The Complete Poetical Works of John Greenleaf Whittier, a historical songbook transcribed on Wikisource and reproduced from the pinned revision linked below.
As Islam’s Prophet, when his last day drew
Nigh to its close, besought all men to say
Whom he had wronged, to whom he then should pay
A debt forgotten, or for pardon sue,
And, through the silence of his weeping friends,
A strange voice cried: “Thou owest me a debt,”
“Allah be praised!” he answered. “Even yet
He gives me power to make to thee amends.
O friend! I thank thee for thy timely word.”
So runs the tale. Its lesson all may heed,
For all have sinned in thought, or word, or deed,
Or, like the Prophet, through neglect have erred,
All need forgiveness, all have debts to pay
Ere the night cometh, while it still is day.