Upali was one of the chief followers of the Jain master, Mahavira. Because of his intelligence, Upali often appeared in public debates on behalf of the Jains.
There was one incident where Upali had a debate with the Buddha. At the end of the debate, Upali was so impressed with the Buddha's teachings that he asked to be the Enlightened One's follower. "Venerable Sir, please allow me to be your follower".
To that, the Buddha answered, "Upali, you are at the height of your emotions. Go home and reconsider it carefully before you ask me again".
Upali was extremely impressed, "If it was any other guru, he will parade a banner saying, 'Mahavira's chief lay-disciple has become my follower'. But you, Venerable Sir, you asked me to go home and reconsider. Now, I want to be your follower even more. I will not stand up until you accept me".
Finally, the Buddha agreed to accept Upali, under one condition, "Upali, as a Jain, you have always given alms to Jain monks. When you become my follower, you will CONTINUE to give alms to Jain monks. This is my condition".
Upali agreed to this condition. He became one of the Buddha's disciples.