The blemish of the yam is the blemish of the knife...

[Fagbemijo]

Yoruba: Ìbàjẹ́ iṣu nìbàjẹ́ ọ̀bẹ; ẹni tó ṣe ìbàjẹ́ èèyàn-án ṣe ìbàjẹ́ ara ẹ̀.
English: The blemish of the yam is the blemish of the knife; whoever besmirches other people's names besmirches his/her own.
-Yoruba Proverb