First of all, it should be clear that the preservation of the human species is unquestionably the primary objective of marriage, and such preservation of the species requires continued reproduction. Accordingly, Islam encourages having many children and has blessed both male and female progeny. However, it allows the Muslim to plan his family due to valid reasons and recognized necessities.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
“Marriage in Islam is based not on one single objective or purpose such as procreation or sexual fulfillment. Rather, it is intended to cater to multiple purposes which include, above all, spiritual tranquility and peace, and cooperation and partnership in fulfilling the divine mandate. Let me explain this briefly.
Islam, being a natural way of life, takes into account all of genuine human instincts such as physical, spiritual, intellectual, emotional, et cetera. It is for this reason that, unlike some other religious ideologies, Islam looks at sexuality positively. In other words, instead of attaching any taboo to sexual fulfillment, Islam teaches us to celebrate sexuality within the framework of a lawful union.

The Prophet (peace and blessings be upon him) said, “You merit rewards of charity in your sexual union with your spouses!” His companions asked in surprise, “How shall we getting rewards for fulfilling our natural instincts?” He asked, “What if someone were to fulfill his desire unlawfully; would he/she be punished for doing so?” They replied, “Certainly.” Then he said, “Likewise, when one does it within the framework of marriage, he/she will be rewarded for it!”

Although sexuality is one of the main purposes of marriage, it is not the sole one. According to the clear statement of the Qur’an, tranquility and peace through a successful union is considered the primary objective of marriage: “Among His signs is that He created for you spouses of your own kind in order that you may repose to them in tranquility and He instilled in your hearts love and affection for one another; verily, in these are signs for those who reflect (on the nature of the reality).” (Ar-Rum: 21).

In another place, Allah refers to the relationship between males and females in terms of partnership for achieving goodness and fulfilling the divine mandate for their lives. “The believers, males and females, are partners of one another; they shall jointly enjoin all that is good and counsel against all that is evil.” (At-Tawbah: 71). And procreation of the human species is also another important purpose, although marriage is still valid if, for one reason or another, the stated purpose of procreation cannot be achieved.
Now coming to the issue of birth control, there is nothing in Islam that prohibits it so long as it is done consensually for valid reasons such as the following: putting off pregnancy until such time when the spouses are in a better position to shoulder the responsibilities of parenting, to allow for space between pregnancies in order to provide proper nurturing and care to existing children, et cetera.

Birth control is, however, forbidden or undesirable when it is resorted to as a permanent measure to prevent conception altogether; likewise, it is forbidden if resorted to for fear of poverty. Allah says, “Don’t kill your children for fear of poverty; it is We who provide sustenance for them and you; verily killing them is a most heinous crime!” (Al-Isra’: 31). After reflecting on this verse, scholars have concluded that practicing birth control for fear of poverty is unlawful since it implies weakness of faith and trust in Allah as the Provider and Sustainer of all beings.”