From the 《
乐府诗集·
君子行》 (Yuefu folk poetry anthology, 'Song of the Gentleman'):
君子防未然,不处嫌疑间。瓜田不纳履,李下不整冠 - 'The gentleman guards against what has not yet happened; he does not linger in places of suspicion. In a melon patch he does not adjust his shoe; under a plum tree he does not straighten his cap.' Bending to tie a shoe among melons or reaching up under plums would look like stealing, even if innocent.