Synergism is...the [erroneous] doctrine that there are two efficient agents in regeneration, namely the human will and the divine Spirit, which, in the strict sense of the term, cooperate. This theory accordingly holds that the soul has not lost in the fall all inclination toward holiness, nor all power to seek for it under the influence of ordinary motives...To put it simply, synergism is the belief that faith is produced by our unregenerated human nature...
The Century Dictionary
I say that man, before he is renewed into the new creation of the Spirit's kingdom, does and endeavours nothing to prepare himself for that new creation and kingdom, and when he is re-created has does and endeavors nothing towards his perseverance in that kingdom; but the Spirit alone works both blessings in us, regenerating us, and preserving us when regenerate, without ourselves...
Martin Luther from Bondage of the Will pg. 268
Faith in the living God and his Son Jesus Christ is always the result of the new birth, and can never exist except in the regenerate. Whoever has faith is a saved man.
C.H. Spurgeon from "Faith and Regeneration"
Related: Prevenient Grace - Monergism vs. Synergism - The Doctrine of Regeneration - Free Will