to remain principled and morally pure despite being in a corrupt or filthy environment

他在贪腐成风的官场中依然能够出淤泥而不染，始终坚持清廉。

to grow out of the mud without being stained, typically referring to the physical purity of a lotus

莲花出淤泥而不染，被世人赞誉为花中君子。