A cousin of Mirza Ghulam Ahmad and one of his childhood friends, Imam-ud-Din, became a mystic and was venerated by the Sweeper Community of Punjab as the re-incarnation of Lal Beg. Imam-ud-Din started an annual mela (festival) in Qadian where the Sweeper Community gathered and food was served. This was known as the Chuhra Mela (Festival of Sweepers).
This was the inspiration behind Jalsa Salana (annual convention) that was put in place by Mirza Ghulam Ahmad and he would proclaim about how more people came to his convention compared to those that came to his cousin's.
So, who was Lal Beg? He was a semi-mythical saint of the sweeper community (halalkhors) http://www.maharashtra.gov.in/pdf/gazeetter_reprint/Poona-I/population_dhors.html#.
This saint was a mixed Hindu, Sikh and Muslim reverence and quite popular in the Punjab Legends of the Punjab http://books.google.com/books?id=2xGRlF8MfJAC&pg=PA529&source=gbs_toc_r&cad=0_0&sig=ACfU3U25sQxjRg4Uwo87PG0f7j_YRmckvw
Dr. Bhagvan Das says (http://www.insaf.net/pipermail/insafny_insaf.net/2005-February/000885.html)
Q: Who was Lal Beg?
A: Some say that Lal Beg was actually Lal Bhikku, who could have been a Buddhist saint. If you read the prayers of the sweeper community of northern India which are dedicated to Lal Beg you get a very interesting picture. These prayers are called Kursi Namas. They were collected together by Youngson and published in The Indian Antiquaries. They read like the first book of the Genesis in the Old Testament, tracing the lineage of our heroes. The Kursi Namas very clearly tell us that the sweepers are neither Hindus nor Muslims. There is no mention of any Hindu gods like Rama or Krishna in them. But, very interestingly, the Kursi Namas all begin with the Qur'anic invocation Bismillah-ir-Rahman-ir-Rahim ('In the Name of Allah, the Most Merciful, the Most Compassionate'), which is the standard Islamic form with which every verse of the Qur'an but one begins. And, they all end with the cry, which again is very Islamic, of 'Bolo Momino Vohi Ek Hai!' [ Say, O believers, that He alone is the One True Being! ].
Now, at several places in the Kursi Namas, the names Lal Beg and Bala Shah are used interchangeably. Bala Shah was a leading Punjabi Sufi saint. The Punjabi Sufi Waris Shah writes in his Heer, which is really an encyclopedia of the Punjab of his times, that Bala Shah was the Pir or Sufi preceptor of two so-called low castes, the sweepers or Chuhras and the Pasis Bala Pir Ai Churiyan Pasiyan Da.
Q: Are the sweepers still aware of this tradition?
A: Unfortunately, very few are, and this tradition is fast disappearing. One reason is because Hindu organisations have been sparing no effort to absorb the sweepers into the Hindu fold so as to increase Hindu numbers. They were afraid that otherwise the sweepers would all convert to Christianity, a process that began in 1873 and continued right until 1931. So, they used all means to prevent the conversion of the sweepers. As part of this broader agenda, they started selling the story that the sweepers are actually Valmikis, descendants of Valmiki, the author of the Ramayana. In order to convince the sweepers of their claims, they argued that Bala Shah, the other name for Lal Beg, was actually just a corrupted form of the name Valmiki.