Abu 'Abd al-Rahman al-Sulami noted the following hadith that was recorded as having been transmitted by Ruwaym, "Anas ibn Malik reported that a man in the presence of the Prophet (SAWS) cursed a flea. Then the Prophet stated, 'Do not curse it, because it has awakened one of the prophets for prayer.' "
Sulami reported that Ruwaym said, "It is safer for you to sit with all [other] classes of people than it is for you to sit with Sufis. All people sit in accordance with "customary forms" (rusum), while Sufis sit in accordance with the truths (haqa'iq). All the people require their selves [to be in accord] with the outer dimensions of the law (zawahir al-shar'), while the Sufis require their selves [to be in accord] with the truth of "spiritual caution" (wara') and with constant "sincerity" [toward God] (sidq). So whoever sits with them and opposes them concerning anything the truth of which they have actualized, God will remove the light of faith from his heart.
[Note that the word "truth" here means the "deepest level
of reality" --translator.]