Facetiae, here published as Facetia Erotica. (source)
A peasant of our district, a stupid devil, who was utterly ignorant in matters of sex, got married. Thus it happened one night that his wife turned her back to him in bed, so that her buttocks rested in his lap. He had his weapon ready and landed by chance right in the goal. Marveling at his success, he inquired of his wife if she had two openings. And when she answered in the affirmative, he cried: “Hoho! I am content with but one; the second is entirely superfluous.” Upon which the sly woman, who was secretly consorting with the local priest, replied: “Then we can give the second away to charity. Let us grant it to the church and our priest.” The peasant, thinking to be relieved of an unnecessary burden, agreed [read the rest].