Who is a Sufi you might ask. Below is the answer from Sidi Ahmad Zarruq, a Moroccan Shadhili Shaykh who lived between 1442 to 1493 CE. Translated by Zaineb S. Istrabadi, the following paragraphs are part of Principle 3 and Principle 4 of Qawaid al Tasawuf (Principles of Sufism) which Zarruq authored.
I feel that whosoever has a measure of sincerity in turning towards God has a measure of Sufism, and that the Sufism of everyone is the sincerity of his turning towards God. So, understand this!
The sincerity of turning towards God is conditioned by its being pleasing to God Most High or by that which pleases Him. That which is conditioned is invalid without its condition.
"He approves not unthankfulness from His servants:" so faith is a conditioned that must be fulfilled. "If ye are thankful, He will approve it in you:" so submission is a condition that must be fulfilled.
Thus there is no jurisprudence without Sufism because divine exoteric rules can be known only through jurisprudence. Nor is there any jurisprudence without Sufism for action cannot be carried out without sincerity and turning towards God. Nor can jurisprudence and Sufism be without faith, since neither of the two is valid without it. So all three are necessary because they are attached to one another in principle as souls are attached to bodies: souls have no existence without bodies just as bodies have no life without souls. So, understand this!
Along these lines is the saying of Malik (may God have mercy on him): 'He who follows the path of Sufism while neglecting jurisprudence is a heretic; and he who learns jurisprudence while neglecting the Path commits transgression. But he who combines both, has attained realization.
I maintain that the first is a heretic because of his belief in the doctrine of predestination, which leads to the negation of divine wisdom and general rules. The second committed transgression because his deeds lack any turning towards God through divine wisdom and general rules, a turning that veils him from disobeying God, and also because his deeds also lacks sincerity, which is a condition in acting for God's sake. The third attains to the realization of the Truth in that very same act of holding on to the Truth. So, know this!
ZARRUQ is a nickname given by his grandfather. Derived from azraq ("blue"), his grandfather (or posssibly Zarruq too) had the Berber blue eyes. His parents had died when he was 1 week old, baby Zarruq was then brought up by his maternal grandmother, a saint of Fez, Umm al-Banin.Source: Zaineb S. Istrabadi's Ph.D thesis dated 1988.