Q: I married one of my relatives in Rabi` Al-Awwal, 1385 A.H. When I married her, she was breastfeeding her daughter whom she had from her ex-husband. Her daughter was two years old at that time. My sister-in-law had given birth to a boy a month after her sister's marriage. Many years later, my wife and I had other daughters. When their cousin grew up, he proposed to one of them, and I agreed. However, a few days after the engagement, rumors spread (Part No. 21; Page No. 138) that
the boy was breastfed by his aunt while she was breastfeeding her daughter.
So, I asked my wife about this, and she swore to me that it never happened, and that they lived together at their uncle's house.
If the situation is as you mentioned, that your wife did not breastfeed her nephew, and that your daughter was not breastfed by her aunt, it is permissible for your daughter to marry her cousin. Rumors are not taken into account; what matters is the truth.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.