The Story of Upali

(as told by Ven. Narada in The Buddha and His teachings)
On one occasion Upali the millionaire, a follower of Nigantha Nataputta, approached the Buddha and was so pleased with the Buddha's exposition of the Dhamma that he instantly expressed his desire to become a follower of the Buddha. But the Buddha advised him, saying--"Of a verity, O householder, make a thorough investigation. It is well for a distinguished man like you to make a thorough investigation."
Upali, who was overwhelmed with joy at this unexpected utterance of the Buddha. said: "Lord, if I had become a follower of another teacher, his followers would have taken me round the streets in procession proclaiming that such and such a millionaire had renounced his former religion and had embraced theirs. But, Lord, you advise me to investigate further. The more pleased am I with this salutary advise of yours." And he appreciatively repeated--for the second time, "I seek refuge in the Buddha, the Dhamma, and the Sangha."
Though Upali became a Buddhist by conviction, the Buddha, quite in keeping with his boundless compassion and perfect tolerance, advised him to support his former religious teacher in accordance with his practice.