I knew he had slaves, and asking his brother was told he intended to leave them as slaves to his children.

As writing was a profitable employ, and as offending sober people was disagreeable to my inclination, I was straitened in my mind, but as I looked to the Lord he inclined my heart to his testimony; and I told the man that I believed the practice of continuing slavery to this people was not right, and that I had a scruple in my mind against doing writings of that kind; that, though many in our society kept them as slaves, still I was not easy to be concerned in it, and desired to be excused from going to write the will.

I spoke to him in the fear of the Lord; and he made no reply to what I said, but went away: he also had some concerns in the practice, and I thought he was displeased with me.
In this case I had a confirmation, that acting contrary to present outward interest from a motive of Divine love, and in regard to truth and righteousness, opens the way to a treasure better than silver, and to a friendship exceeding the friendship of men." From 1753 to 1755, two circumstances of a similar kind took place, which contributed greatly to strengthen him in the path he had taken; for in both these cases the persons who requested him to make their wills were so impressed by the principle upon which he refused them, and by his manner of doing it, that they bequeathed liberty to their slaves.
In the year 1756, he made a religious visit to several of the society in Long Island.

Here it was that the seed, now long fostered by the genial influences of Heaven, began to burst forth into fruit; Till this time he seems to have been a passive instrument, attending only to such circumstances as came in his way on this subject.

But now he became an active one, looking out for circumstances for the exercise of his labours.
"My mind," says he; "was deeply engaged in this visit, both in public and private; and at several places, observing that members kept slaves, I found myself under a necessity, in a friendly way, to labour with them, on that subject, expressing, as the way opened, the inconsistency of that practice with the parity of the Christian religion, and the ill effects of it as manifested amongst us." In the year 1757, he felt, his mind so deeply interested on the same subject, that he resolved to travel over Maryland, Virginia, and North Carolina, in order to try to convince persons, principally in his own society, of the inconsistency of holding slaves.