Abdul Qadir Gilani (God be pleased with him) who was known for being the founder of Qadiriyya tariq (Sufi order) said:

Get out from your own self and be away from it and be a stranger to your sense of self. Surrender everything to God and become His gatekeeper at the door of your heart and keep His commandments by admitting whomever He permits to be admitted, and honour His prohibition by keeping out everything which He forbids so as not to allow the desire of the flesh to get into your heart after it has gone out of it. And to expel the desire of the flesh from the heart one has to put up resistance to it and refuse subordination to it in all conditions; and to admit it into the heart means to acknowledge subordination to it and to make alliance with it. So, do not will anything which is not the will of God. Any will of yours which is not the will of God is a desire of the flesh, which is, so to say, the wilderness of fools and it is death for you and a cause of falling away from the sight of God and of screening Him away from yourself, if you are in this wilderness. Always guard the commandment of God and abstain from His prohibitions and surrender to Him always in all that He has ordered and do not associate with Him anything from His creation. Thus your will and your desires and your passions are all His-creations. So do not will anything nor desire anything nor indulge in any passion so that you may not prove to be a polytheist. God says: 

فَمَن كَانَ يَرْجُو لِقَاءَ رَبِّهِ فَلْيَعْمَلْ عَمَلًا صَالِحًا وَلَا يُشْرِكْ بِعِبَادَةِ رَبِّهِ أَحَدًا

So whoever hopes to meet his Lord, he should do good deeds, and join no one in the service of his Lord. (Qur’an 18:111) 

Polytheism consists not merely of idol-worship. It is also polytheism to follow the desire of the flesh and to adopt anything of this world and of the hereafter in association with God. Because whatever is besides God is not God. Thus when you are engaged in anything which is besides Him you are undoubtedly associating that other thing with God. Therefore, beware and do not rest, and fear and do not feel secure, seek and do not remain indifferent; then alone will you attain to security. (The Seventh Discourse, Futuh al-Ghaib)