Regarding Breast-feeding in Which There Exists Doubt

Question :

I submitted a proposal of marriage to a girl four months ago and the Qiran contract was made. But I have not consummated the marriage with her according to the Islamic Law. And this year one of my sisters informed me that she had breast-fed this girl, but she did not remember how many times it had occurred, due to the fact that a long time approximately twenty years has passed. So is it permissible for me to marry this girl?

Answer:

The marriage contract completed with this woman is correct and it is not invalidated except by clear, positive proof.

Breast-feeding in which there exists doubt or whose number is uncertain has no effect, according to the words of 'A'ishah, may Allah be pleased with her, who said: "It was revealed in the Qur'an that ten known breast-feedings caused prohibition, then it was abrogated by five known breast-feedings."

The description of the breast-feedings as being "five known breast-feedings" is a proof that it must be known that the breast-feeding took place, and it must also be known how many times it occurred.

If the woman who breast-fed is unsure whether or not she completed five or not, then there is no effect from this suckling, therefore, your sister's statement results in no harm upon the marriage you made with this woman.

Source:
Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 6 Pages 158-159