Assalamualaikum There are many people in South Asia who claim to be Syeds. Whether this claim is true or not is a different thing, but some of them say that it is haraam for a female Syed to marry a non-Syed boy. They say that Syed girls have the status of mothers (and according to some, sisters) of non-Syeds. I believe that Islam doesn't accept caste-based discrimination, but I want proofs from the Quran and Sahih Hadith to correct them.
Alaikumassalam wa rahmatullah,
That has no basis in Islam. Syeds claim descent from the grandsons of the Prophet 
, and we know that the daughters of these grandsons married people unrelated to the Prophet’s family . If that was acceptable for them, it should be acceptable for all descendants of the Prophet . There is nothing in the Quran or Sunna that prevents the descendants of the Prophet from marrying non-descendants.