Pope Leo the Great writes to Bishop Rusticus of Narbonne (458/9)

The law of continence is the same for the ministers of the altar, for the bishops and for the priests; when they were (still) lay people or lectors, they could freely take a wife and beget children. But once they have reached the ranks mentioned above, what had been permitted is no longer so

Question 3. Concerning those who minister at the altar and have wives, whether they may lawfully cohabit with them?

INQUIS. III.
De his qui altario ministrant et conjuges habent, utrum eis licito misceantur?

Reply. The law of continence is the same for the ministers of the altar as for bishops and priests, who when they were laymen or readers, could lawfully marry and have offspring. But when they reached to the said ranks, what was before lawful ceased to be so. And hence, in order that their wedlock may become spiritual instead of carnal, it behoves them not to put away their wives but to “have them as though they had them not,” whereby both the affection of their wives may be retained and the marriage functions cease.

RESP. Lex continentiae eadem est ministris altaris quae episcopis atque presbyteris, qui cum essent laici sive lectores, licito et uxores ducere et filios procreare potuerunt. Sed cum ad praedictos pervenerunt gradus, coepit eis non licere quod licuit. Unde, ut de carnali fiat spirituale conjugium, oportet eos nec dimittere uxores, et quasi non habeant sic habere, quo et salva sit charitas connubiorum, et cesset opera nuptiarum.