I found this story on @HistoryWeird's blog here. The original source was a letter from the Earl of Chesterfield to Philip Stanhope, October 19 1753.
"Philip Dormer Stanhope (1694-1773) was an English Whig politician and, from his father’s death in 1726, the fourth Earl of Chesterfield . . . Stanhope’s best known literacy legacy was a collection of letters he wrote to his son, also named Philip, during the 1740s and 1750s. Most of Stanhope’s letters are informative, educational and advisory, an attempt to prepare his son for the earldom – however he occasionally lapsed into whimsy.
"In October 1753 Stanhope penned a long missive to Philip Junior that explored Jewish culture, Turkish history and how to conduct oneself around women. Stanhope interrupted this lecture to tell his son he had purchased a new dog:
"'I have had a barbet [water dog] brought me from France, so exactly like [your dog] Sultan that he has been mistaken for him several times, only his snout is shorter and his ears longer than Sultan’s. [I] have acquired him the name of Loyola… My Loyola, I pretend, is superior to your Sultan… I must not omit too that when he breaks wind, he smells exactly like Sultan.'"