I need a quote from Ignatius Sancho on abolitionism.

Ignatius Sancho (1729–1780), who was born on a slave ship bound for England and worked as a slave until he eventually escaped, is famous today for his published letters, in which he eloquently expressed his thoughts on the evils of slavery.
Sancho essentially set himself free by escaping from his slaveholders, and his self-taught expertise as a writer positioned him as an outspoken critic of slavery.
It’s important to note that, though Sancho certainly would have agreed that slavery must be abolished, his works do not generally touch on the idea of abolition or abolitionism directly. (Abolition is the act of legally doing away with the system of slavery, and abolitionism is the idea or philosophy that slavery must end and that slaves must go free.)
As far as my research has uncovered, the closest that Sancho appears to come to outright calling for abolition is when he wrote an urgent appeal to a famous author, Laurence Sterne, for Sterne to write more about abolition. This urging appears in a publication titled Letters of the Late Ignatius Sancho, an African, specifically in letter XXXV:

The subject [of abolition], handled in your striking manner, would ease the yoke (perhaps) of many.

So, in lieu of finding Sancho’s explicit comments on abolitionism, let’s explore some of his statements that condemn slavery.
Here’s something Sancho wrote to a friend of his:

In Africa, the poor wretched natives blessed with the most fertile and luxuriant soil- are rendered so much the more miserable for what Providence meant as a blessing: the Christians’ abominable traffic for slaves and the horrid cruelty and treachery of the petty Kings encouraged by their Christian customers who carry them strong liquors to enflame their national madness – and powder – and bad fire-arms – to furnish them with the hellish means of killing and kidnapping.

As you can see, Sancho’s writing style is balanced and eloquent, his words carefully chosen, his tone as dramatic and intense as the subject matter demands. In the quote above, Sancho calls attention to the ostensibly “Christian” nature of the slave traffickers, pointing out how cruel and detestable their actions are. With his use of alliteration, and with his careful placement of the most explosive words at the very end of his sentence, Sancho draws the reader’s attention to the “killing and kidnapping” that constitutes slavery—a prelude to an outright claim that it must be abolished.
Here, Sancho continues to condemn the odious effects of slavery as he addresses a friend’s son:

In some one of your letters which I do not recollect - you speak (with honest indignation) of the treachery and chicanery of the natives. - My good friend, you should remember from whom they learnt those vices: - the first Christian visitors found them a simple, harmless people - but the cursed avidity for wealth urged these first visitors (and all the succeeding ones) to such acts of deception - and even wanton cruelty - that the poor ignorant Natives soon learnt to turn the knavish - and diabolical arts which they too soon imbibed - upon their teachers.

Above, Sancho acknowledges the corruptive influence of slavery on the slaves themselves as well as on their “Christian” captors, again calling attention to the excessive greed of the slaveholders. Notice the heavy religious tone of Sancho’s statement, which is evident in his choice of words like “cursed” and “diabolical.”
For more examples of Sancho’s eloquent condemnations of empires and of slavery as a practice, please refer to the links below.
http://www.brycchancarey.com/sancho/letter4.htm

https://ia802503.us.archive.org/32/items/lettersoflateign00sanc_0/lettersoflateign00sanc_0.pdf

https://publicdomainreview.org/collection/letters-of-the-late-ignatius-sancho-an-african-1784/