Is it permissible to marry the daughter of a maternal aunt if the grandmother (mother's mother) breastfed the suitor an unknown number of times or to an unknown extent of satiation, knowing that the only maternal aunt who witnessed the breastfeeding was a child at the time, and the mother did not witness the breastfeeding nor know its details?

If it is confirmed that the questioner nursed five full (suckling) feeds from his grandmother (his mother's mother), then it is forbidden for him to marry the daughters of his maternal uncles and paternal aunts. This is because he becomes a maternal uncle to the daughters of his paternal aunts and a paternal uncle to the daughters of his maternal uncles through fosterage, based on the Prophet's (peace and blessings be upon him) saying: "Fosterage prohibits what lineage prohibits." The testimony of a single trustworthy woman is sufficient to establish fosterage. If the nursling was six months old at the time of nursing, it does not matter whether the nursing occurred before or after weaning, as what matters is the period of two years, not weaning itself. Furthermore, the paternal aunt's lack of knowledge regarding the feeds being full does not matter, as what matters is the completion of each suckling. So, once it is established that there were five or more sucklings, they are considered as full feeds. Therefore, he must refrain from marrying his paternal aunt's daughter.