"There are three blessings arising from Matrimony, if it be made a good use of, viz : Children, fidelity, and the grace of the sacrament. The generation of children, together with their proper education, must be had in view, if we would make a good use of matrimony ; but on the contrary, he commits a most grievous sin, who seeks only carnal pleasure in it. Hence Onan, one of the children of the patriarch Juda, is most severely blamed in Scripture for not remembering this, which was to abuse, not use the holy Sacrament. But if sometimes it happen that married people should be oppressed with the number of their children, whom through poverty they cannot easily support, there is a remedy pleasing to God; and this is, by mutual consent to separate from the marriage-bed, and spend their days in prayer and fasting. For if it be agreeable to Him, for married persons to grow old in virginity, after the example of the Blessed Virgin and St. Joseph, (whose lives the Emperor Henry and his wife Chunecunda endeavoured to imitate, as well as King Edward and Egdida, Eleazor a knight, and his lady Dalphina, and several others,) why should it be displeasing to God or men, that married people should not live together as man and wife, by mutual consent, that so they may spend the rest of their days in prayer and fasting?"
--St. Robert Bellarmine, The Art of Dying Well CHAPTER XV. THE FIFTEENTH PRECEPT, ON MATRIMONY.
"But this kind of chastity is also to be observed, that sexual intercourse must not take place heedlessly and for the sake of mere pleasure, but for the sake of begetting children. And since this observance is found even amongst some of the lower animals, it were a shame if it be not observed by men, reasonable, and worshipping God."
--Clement of Alexandria, Recognitions of Clement. Chapter XII: Importance of Chastity
Saint Caesar of Arles: “As often as he knows his wife without a desire for children… without a doubt he commits sin.”
Errors Condemned by Pope Innocent XI: “9. The act of marriage exercised for pleasure only is entirely free of all fault and venial defect.”–Condemned
Those that be married must examine themselves in particular, if in their mind thinking of other persons, or with intention not to beget children, but only for carnal delight, or with extraordinary touchings and means, they have sinned against the end, and honesty of marriage. -- Ven. Luis de Granada. A SPIRITVAL DOCTRINE, CONTEINING A RVLE To liue vvel, vvith diuers Praiers and Meditations p. 362 (A Spiritual Doctrine, containing a rule to live well, with divers prayers and meditations)
"Married people were shown the nobility of their calling and he exhorted them to fulfill holily its duties. A lady of the name of Ruet, of Ouroux, in the department of the Rhone, had already a large family and was about to become a mother once more. She came to Ars in order to seek courage at the feet of its holy Cure. She had not long to wait, for M. Vianney summoned her from amid the crowd. "You look very sad my child." he said, when she was on her knees in his confessional. "Oh! I am so advanced in years Father!" He comforted , "my child... if you only knew the women who will go to hell because they did not bring into the world the children they should have given to it."
"Come now my little one, he said with fatherly kindliness to the woman who confided to him her anxiety because of her large family. "do not be alarmed at your burden, our Lord carries it with you. The good God does well all that he does: when he gives many children to a young mother it is that he deems her worthy to rear them. It is a mark of confidence on his part."
Page 311-312 of The Cure D'Ars - Trochu.