I was listening to a video of Dr Zakir Naik in which he mentions about a saying of Prophet Muhammad not to marry first cousins generations after generations in a family repeatedly as it increases the risk of genetic disorder. I would like to know if there is really a Hadith against the same.
بسم الله الرحمن الرحيم
(Fatwa: 779/778/N=08/1437)
I could not find out any such authentic Hadith in the collection of Hadith. Had you quoted the reference of any Hadith book we would have written something regarding its status of Sanad or Matan.
Note:Zakir Naik is deviant in view of his thoughts and is misguiding others. You cannot trust his explanation of Quran and Hadith. Hence common Muslims should not listen or watch his audio or video, and none of his book or written things should be read so that one is saved from his false and baseless and misguiding thoughts.
قال ابن سيرين : إن هذا العلم دين فانظروا عمن تأخذون دينكم (مقدمه مسلم شريف، ص 11، مطبوعه: مكتبه اشرفيه ديوبند)
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband