I am a practicing Muslim who tries his best (with several shortcomings)to live a life of servitude to Allah (swt). Recently my brother introduced me to the teachings of Eckhart Tolle through the book the "Power of Now". This was one of the most eye opening books I have ever read, probably the most influential after the Quran itself. I found what he says about being in the present moment and the illusion of the ego (nafs) to be very compatible with the teachings of Islam. I found after reading it and trying to live by it that I get far less distracted in my Salah (prayer), and I don't stress too much about the future or regret about the past, or have hatred for others (having identified all of these as the evil which the nafs commands as Allah tells us in Surah Yusuf).
When I asked a scholar I know just about the concept of mindfulness and its origin in Zen buddhism, he said there is nothing wrong with adopting it. He said the Islamic viewpoint was that such teachings have prophetic origins even if we don't know the specific prophet which taught it.
But at the same time, Eckhart in his book talks about our "true self". The essence of us that lies beyond the ego, and he somehow equates this with God. I think this delves into the realm of wahdat-ul-wujud and the teachings of Ibn Arabi. The danger I think with adopting this belief is if you believe the Creator is in you then what is the purpose of worship?
So I just want to know which teachings from Tolle's Book and Zen Buddhism can Muslims adopt and which should they be careful of lest it corrupts their Aqeedah?