Shaykh ul-Islam (May Allah have Mercy on him):
So indeed a person may know that the truth is with other than him and, in spite of this, he rejects that due to his envy of him or due to seeking to be above him or due to the desire of the soul. And that desire causes him to transgress against him, reject that which he says by any way whilst in his heart, he knows that the truth is with him.
Source: Majmoo al Fataawa, vol 7, pg 191
قال شيخ الإسلام (رحمه الله) فإن الإنسان قد يعرف أن الحق مع غيره ومع هذا يجحد ذلك لحسده إياه, أو لطلب علوه عليه أو لهوى النفس, ويحمله ذلك الهوى على أن يعتدي عليه ويرد ما يقول بكل طريق وهو في قلبه يعلم أن الحق معه