Abu 'Umar az-Zajaajee rahimahullah, who was from among the companions of al-Junaid rahimahullah, Sufyaan ath-Thauree rahimahullah and others, said:
"In the days of ignorance, the people used to follow whatever their intellects and temperaments considered good. The Prophet sallallaahu 'alayhi wasallam came and directed them towards the Sharee'ah and emulation. A sound intellect is therefore one which considers good whatever the Sharee'ah considers good, and abhors whatever the Sharee'ah abhors.[The Sunnah way of the Sufis]"