One time there was a small gathering of some of the Buddha’s disciples. In front of this gathering, the Buddha asked Shariputra, “Do you accept on faith the fact that meditation can lead to the attainment of nirvana?” Shariputra answered that he did not accept this teaching on faith, and that only those who have not personally realized this truth need to accept it simply because it is taught by the Buddha.
The disciples who witnessed this criticized Shariputra, saying that he did not have faith in the Buddha. But the Buddha praised Shariputra for his answer. He explained to the disciples that they, too, must come to understand the Dharma through their own personal experience.
This is the backstory (as given by Buddhaghosa) to verse 97 of the Dhammapada.