I have unprotected intercourse with my wife but I fear that my wife will become pregnant. We have four children with an age gap of two years between each child. My wife is a full-time mum, she looks after everything related to the kitchen, school runs etc. so it will be very tough for us to have more children. Please guide me on whether she can use contraceptives or birth control pills.
بسم الله الرحمن الرحيم
In The Name Of Allah, The Most-Gracious, The Most-Merciful
It is well documented in the authentic ahadith that contraception in the form of coitus interruptus was performed during the time of the Prophet (pbuh), and he did not forbid it.
Narrated Jabir (ra) added: “We used to practice coitus interrupt us during the lifetime of Allah's Messenger (ﷺ) while the Qur'an was being Revealed.” 
In Bada’i as-Sana’i it explains that it will be permitted to perform coitus interruptus without any dislike, when the wife agrees to it because this is linked to her rights.
Therefore, based on this, using modern forms of reversible contraceptives or birth control is permitted, without any dislike, if both you and your wife agree to it.
It should be noted that permanent forms of contraception will be prohibited as the Prophet forbade castration – a permanent contraceptive.
Only Allah knows best
Written by Alimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Sahih Bukhari, Hadith Number 5209
 Imam Kassani, Al-Bada’i As-Sana’i, Volume 2, Page 334
 Ibn Abideen, Raddul Muhtaar, Volume 6, Page 38