Ahsanallahu ilaykum Is the saying "judge the sin not the sinner" from Islam?

It is not a hadith, and as an unqualified principle it is not correct. The scholars state that a Muslim who disobeys is loved in respect of his iman and disliked in respect of his disobedience at the same time, so you neither drop your dislike of what he does nor strip him of the love owed to him for his iman.