Huldrych Zwingli, who had slept with a woman in a former parish, petitioned his ordinary, Bishop Hugo von Hohenlandenberg of Constance, for permission to marry, which was denied.  Zwingli was also secretly married to a widow, Anna Reinhart — as many people knew. 
 Zwingli explains his brief affair with the daughter of a barber in Einsiedeln in a letter to Heinrich Utinger in Zurich dated December 5, 1518. See Huldreich Zwinglis Samtliche Werke, vol. 7, ed. E. Egli, G. Finsler, and W. Kohler, Corpus Reformation 94, (Leipzig: M. Heinsius Nachfolger, 1911), pp. 110-13 . . .
 G.R. Potter, Zwingli (Cambridge: Cambridge University Press, 1976), pp. 78-81. Frau Reinhart had been Zwingli’s concubine before their marriage. Their secret marriage was publicly announced before the birth of their first child.
(David C. Steinmetz, in John H. Van Engen, editor, Educating People of Faith, Grand Rapids, Michigan: Eerdmans Publishing Co., 2003, p. 259 [in the chapter: “Luther and Formation in Faith”] [2nd URL]; footnote numbers changed )
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Zwingli lived in the relation of concubinage as a priest. (James Hastings & John A. Selbie, Encyclopedia of Religion and Ethics, Part 6, New York: Charles Scribner’s Sons, 1911, “Concubinage (Christian)”, p. 818)
Ulrich Zwingli, who began his career as a Catholic priest in Zurich, admitted siring at least one child with his concubine, Anna Reinhard. Such conduct should not be considered gross, he explained, since he had abided by his principle not to seduce a virgin or a nun. (William E. Phipps, Clerical Celibacy: The Heritage, Continuum International Publishing Group, 2006, p. 155 [2nd URL] )
Zwingli was a sensual man. Unlike Luther, he had several sexual misadventures . . . He had indeed had sexual relations with the daughter of a powerful man . . . (Richard Marius: Luther: A Biography, Lippincott, 1974, p. 212 [2nd URL] )
“It is a dangerous thing,” says Zwingli, “for a young priest to have access, through the sanctity of his office, to young women, be they married or virgins . . . ” Zwingli himself, as he writes to his friend Utinger, with the greatest candour, had formed a resolution to live in this regard, as well as in every other, a holy life before God; but alas . . . he fell too before the inroad of fleshly lusts, as he himself, with deep pain and remorse, confessed, for he would not appear better than he really was. (R. Christoffel, Zwingli; or The Rise of the Reformation in Switzerland, translated by John Cochran, Edinburgh: T&T Clark, 1858, p. 13)
Like the clergy about him, he believed himself absolved from the obligation of chastity because bound by the vow of celibacy. Lapses from sexual purity were too common to be considered objections in a priest, but the charge against him was then made that he had seduced a girl of good family . . . He was written to on the subject and his reply is extant. He denied the charge of seduction, but frankly admitted the charge of habitual incontinence, and he does it in a jesting tone which shows that he had no conception that his offense was any other than a trifling one . . . it was, therefore, as a confessedly libidinous man that he came to Zurich . . . (Samuel Macauley Jackson, editor, New Schaff-Herzog Encyclopedia of Religious Knowledge, New York: Funk & Wagnalls, 1912, Vol. XII, “Zwingli”, p. 539)
The European Reformation, Blackwell Publishing, 1996, p. 172 [2nd URL] )Detractors raised the issue of Zwingli’s womanizing. Zwingli responded to the rumor that he had seduced the daughter of an influential citizen by admitting his struggle with sexual temptations but denying both the woman’s “purity” and her father’s influence. “Some three years ago I firmly vowed not to touch any woman, . . . I succeeded poorly in this, however. In Glarus I kept my resolution about six months, in Einsiedeln about a year . . . That girl was a ‘virgin’ during the day and a ‘woman’ at night. She was such a ‘day’ virgin, however, that everyone in Einsiedeln knew exactly her role . . . She had had affairs with many men, finally with me. Or let me say it better: she seduced me with more than flattering words” (Hillerbrand, 1964: 115-16). (Carter Lindberg,
Even Zwingli’s celebrated sexual lapses as a young priest . . . did not overly trouble his conscience. To be sure, he regretted his failure to fulfill his vow of celibacy, but he did not seem to doubt his salvation because of these lapses. His famous defence was that, although guilty of sexual immorality, he had never defiled a ‘virgin, nun or married woman’. (Peter McEnhill & George Newlands, Fifty Key Christian Thinkers, Routledge, 2002, 270-271 [2nd URL] )
He did not let his sacerdotal vows exclude him from the pleasures of the flesh; he had some affairs with generous women. (Will Durant, The Reformation, [volume 6 of 10-volume The Story of Civilization, 1967], New York: Simon & Schuster, 1957, p. 405)
Again 1522 was the year when houses of ill-fame were cleaned out of Zurich at Zwingli’s inspiration. How could that have been done if he were living in such concubinage. . . . Clerical marriages might have been possible in the former days of Catholicism, but not with the awakened conscience of the Protestant Reformation. (Calvinist James I. Good, The Reformed Reformation, Philadelphia: The Heidelberg Press, 1916, 89)
Zwingli argues, in effect: “the vow of celibacy in the priesthood is too tough to uphold; everybody’s violating it, so I may as well do it, too, and if I am called on it, I’ll appeal to the fact that it’s impossible to be celibate and everyone is out there having fun, so why shouldn’t I do so too (young stud and gift to women that I am)! And besides, that evil, wicked woman and ‘day virgin’ in Einsiedeln seduced me!, and hey, I didn’t seduce any virgins, nuns, or married women! So give me a pass, huh [wink, wink]? The problem isn’t my virility, it is the confounded papist and Romish rule of celibacy, and it also depends on what is is.”