In the autumn of the following year, some disputed claims, which his wife had on the estate of her maternal grandfather in Ireland, made it necessary for him to visit that country. Experience had painfully convinced him that theological controversy sometimes leads to personal animosity; and that few people were so open and direct in their mode of expressing hostility, as he himself was. Therefore, before going abroad, he took the precaution to ask letters from citizens of various classes and sects in Philadelphia; and he found no difficulty in obtaining them from the most respectable and distinguished. Matthew Carey, the well known philanthropist wrote as follows: "As you are about to visit my native country, and have applied to me for a testimonial concerning your character, I cheerfully comply with your request. I have been well acquainted with you for about thirty-five years, and I can testify that, during the whole of that time, you have been a perfect pest to our Southern neighbors. A Southern gentleman could scarcely visit this city, without having his slave taken from him by your instrumentality; so that they dread you, as they do the devil." After enjoying a mutual laugh over this epistle, another was written for the public, certifying that he had known Isaac T. Hopper for many years as "a useful and respectable citizen of the fairest character." When Friend Hopper arrived in Ireland, he found many of the Quakers prejudiced against him, and many untrue stories in circulation, as he had expected. Sometimes, when he visited public places, he would overhear people saying to each other, in a low voice, "That's Isaac T. Hopper, who has given Friends so much trouble in America." A private letter from an "Orthodox" Quaker in Philadelphia was copied and circulated in all directions, greatly to his disadvantage. It represented him as a man of sanctified appearance, but wholly unworthy of credit; that business of a pecuniary nature was a mere pretence to cover artful designs; his real object being to spread heretical doctrines in Ireland, and thus sow dissension among Friends. In his journal of this visit to a foreign land, Friend Hopper says: "It is astonishing what strange ideas some of them have concerning me. They have been informed that I can find stolen goods, and am often applied to on such occasions. I think it would be no hard matter to make them believe me a wizard." This was probably a serious version of his pleasantry with the Dutchman about finding his goods by calculating the age of the moon.