Assalaamu alaikum wa rakmatullahi wa barakatuh.
I heard that it is scholarly consensus that the minimum age of viability is 6 months. How can this be the case when in some cases, children are born prematurely before 6 months have passed? In some very rare cases, babies have been born after 23 weeks of pregnancy. Thank you. Jazakhallah Khaeir.

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 is His slave and Messenger.

First of all, you should know that there is no explicit text in the Quran or the Sunnah that the minimum duration of pregnancy is six months, but the scholars concluded this from the Quran.

Ash-Shawkaani said in as-Sayl al-Jaraar:

"There is absolutely no authentic, or Hasan or Dha’eef (weak) evidence attributed to the Prophet that the least period of pregnancy is such and such period; they only provided evidence of the Saying of Allah (what means): {…and his gestation and weaning [period] is thirty months.} [Quran 46:15]; and the Saying of Allah (what means): {… and his weaning is in two years.} [Quran 31:14]

This evidence to which the scholars were inclined to is supported by the fact that it has never been heard from what was reported from the authors of biography and history that a child who was born for less than six months has ever lived. Even in our present age and time, nothing was heard about this. Rather, in general, a child who was born in six-month pregnancy rarely lives but the existence of this rarity indicates that the minimum duration of pregnancy is six months." [End of quote]

What is meant by the minimum duration of pregnancy is the period in which the newborn usually lives without external medical assistance, and this does not conflict with the pregnancy that was born in less than this period and lived, because this type of birth survived thanks to Allah’s Will because of external medical care, and this in not a normal case like all other newborn children. Those who live in our age of these children – who are rarely born in a period of less than six months – is not due to the fact that the minimum duration of pregnancy is less than six months but it is due to the development of medicine and ways of rescuing these premature babies from death, by Allah’s Will.

For more benefit on the minimum period of pregnancy, please refer to Fatwa 283993.

Allah knows best.