In his book, The Attributes of God, A. W. Tozer mentions that John Wesley had a bad relation with his wife and because of this failed marriage, it is said that he (sometimes) used to pray in Latin so that his wife won't understand what he was praying about.
The version of the book I have has no bibliography, so I am looking for the primary source of these affirmations.
Some men have wives that are wildcats—difficult to get along with—and they think they are tempted above all others. John Wesley was married to a wildcat, and she didn’t even have her claws trimmed. But God got John Wesley through all right.
He used to kneel down and pray in Latin so his wife wouldn’t be able to know what he was saying. And while he prayed, she threw old shoes at his head! Not a very nice family affair, but that’s the way they got on.
The time came when Wesley said good-bye to his wife and went off preaching, even though she didn’t want him to. And they never did get together much after that, though he saw to it that she was taken care of.
She stayed home and grumbled as he went out everywhere preaching the gospel and transforming England. Then one day he was riding along on his horse, meditating or praying, looking up in the sky. Someone rode up alongside him and said, “Mr. Wesley, your wife is dead.” And he looked down and said, “Oh, she died, did she?” And he went back to looking up. Wesley got along all right, in spite of the wife he had.
What is the source of the idea that John Wesley used to pray in Latin so that his spouse won't understand?