Reference: Reported by al-Aajurree in ash-Sharee’ah (p57), al-Laalikaa’ee in as-Sunnah (no. 215) and Ibn Battah (no. 586) and it is saheeh
A man came to al-Hasan [al-Basree] and said:
I wish to debate with you about the Religion.
al-Hasan replied:
I know my Religion. If you have lost your Religion go out and look for it.
