A woman put her milk in a boy's ear who grew up and wishes to marry her daughter
It is permissible for the questioner to marry his cousin Hissah. What is mentioned in the question, that
the mother of his fiancée dropped some of her breast milk in his ear once, has no effect on the marriage concerned for it is not breastfeeding. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.