平生不做亏心事，半夜敲门心不惊
píng​shēng​bù​zuò​kuī​xīn​shì​bàn​yè​qiāo​mén​xīn​bù​jīng

rest with a clear conscience

平生不做亏心事，半夜敲门心不惊 平生不做虧心事，半夜敲門心不驚 píng​shēng​bù​zuò​kuī​xīn​shì​bàn​yè​qiāo​mén​xīn​bù​jīng
rest with a clear conscience
Literally "if one does no wrong during one's life, a knock at the door at midnight will not cause alarm"; a clear conscience is the best protection from fear.