People began to claim Syed ancestry enmasse during Mughal rule due to the state benefits allotted to Syeds; specifically exemption from taxation, provision of a hefty allowance and preference in employment.
The actual original Syed population (along with other Arabs) were located in the Arab quarters of Mansura and Multan.
The Arabs/Syeds of Mansura, along with the rest of the population, were massacred and exterminated by Mahmud Ghaznavi.
While the Arabs/Syeds of Multan were exiled to India by Hussain Shah Langah, one of the reasons being the increasing unpopularity of Syeds following a major event where they conspired with an invading Timurid army to open the gates and allowed them to massacre and plunder the inhabitants in return for the Syeds to be spared and their positions be retained.
Hussain Shah Langah was a local tribal leader that had wrested control over South Punjab and had declared independence from the Delhi Sultanate, becoming the Sultan of Multan. The exiled Syeds then had lobbied Delhi to invade South Punjab and return them to power. A massive invasion force was sent which quickly managed to surround and besiege Multan. Hussain Shah Langah, understanding that the city would soon starve, led his Baloch and Punjabi cavalry in a suicidal sally that miraculously managed to break the siege and route the enemy guaranteeing his independence and destroying any hopes of return for the exiled Syeds.