Thank you for the reference.
The Prophet Muhammad (pbuh) did not have any sons, only daughters. Syeds - both Shi'a and Sunni - claim to be descended from the Prophet through his daughter Fatima and his son-in-law Ali (rda).
Sorry, but I absolutely reject the notion that millions upon millions of Syeds in the Indian sub-Continent are the descendants of the Prophet Muhammad (pbuh). There are more Syeds in Pakistan than in the Arab world, or so it seems, and that, in itself, is utterly ridiculous and very revealing. I recall my (Iraqi) friend being astonished when explaining to her that every second person had the name 'Syed' attached to their name in Pakistan.
Because Muslims have adopted and imbibed the concept of the caste system from centuries of contacts with Hindus, they have their own hierarchical system, whereby Syeds sit at the top, and then other 'castes' follow after them.
In any case, even if we accept the ludicrous claim that all these millions are indeed descended from the Prophet, it will not avail them in the least on the Day of Judgement, because family connections or relations cannot save an individual from his/her own actions.