All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
Procreation is one of the most important purposes of marriage in Islam. The texts of the Quran and Sunnah informed us that the provision of all the creation is guaranteed by Allah, The Exalted, and that the provision of a fetus is written for him while it is still in its mother's womb. The Islamic legislation commands the Muslims to beget children because this is what concerns us. However, the provision is provided to us by The Lord of the Worlds. Therefore, permanent birth prevention for fear of poverty or any other reason is impermissible, unless there is a Sharee‘ah-acceptable necessity such as fear of a definite or most likely harm to befall the mother, for example. One should not prevent pregnancy, even temporarily, for fear of poverty. Rather, a Muslim should pursue the available means to procreate children and rely on Allah, The Almighty (for provision). However, there is no sin in preventing pregnancy temporarily.
For more benefit on permanent birth control, please refer to Fatwa 83837.
Allah knows best.