muslim (may allaah have mercy on him) reported that a man ate with his left hand in the presence of the prophet (peace and blessings of allaah be upon him). he said,

“eat with your right hand!” the man said, “i cannot” he said, “may you never be able to!” nothing was stopping him except pride, and he never raised it to his mouth after that. (no. 2021).

according to a report narrated by ahmad: “iyaas ibn salamah ibn al-akwa’ reported that his father told him: ‘i heard the messenger of allaah (peace and blessings of allaah be upon him) telling a man called bisr ibn raa’i al-‘eer, whom he saw eating with his left hand, to eat with his right hand. he said,

‘i cannot.’ he said, ‘may you never be able to!’ and his right hand never reached his mouth after that.” (4/54)

al-nawawi (may allaah have mercy on him) said: “this hadeeth shows that it is permissible to pray against the one who goes against a shar‘i ruling for no good reason. it also demonstrates enjoining what is good and forbidding what is evil in all matters, even in the matter of eating.” (sharh saheeh muslim, 13/192).

we may also note here that the du’aa’ against him was not for something that would help the shaytaan against him, it was for something that was more like a rebuke or telling-off.