Sheikh ul-Islaam Ibn Taymiyyah رحمه الله:
"Ikhlaas cannot be achieved except after having Zuhud, and there is no Zuhud except after having Taqwa, and Taqwa is following the Commands (of Allaah and His Messenger ﷺ) and keeping away from prohibitions."
[Majmuu' al-Fataawa 1/94]
Ibnul Qayyim al-Jawziyyah رحمه الله:
"Sincerity is not combined in the heart along with the love of being praised by the people and being commended by them, and also having greed for what the people have, except like water being combined with fire."