Is it a sin to say the mistakes of a person to his face or to talk behind his back? Is there a hadith related to condemnation?

Dear Brother / Sister,

It is not permissible to say the mistakes of people to their faces in a way to offend them and in the presence of others and to condemn them because of it. To mention them behind a person’s back is a bigger sin since it is regarded as backbiting.   

The following statement is included in our resources as a hadith: "If a person shames his brother for a sin, he shall not die until he himself commits it." (Tirmidhi, Qiyamah, 53, no: 2507; Bayhaqi, Shuabul-Iman, 5/315, no: 2778; see Kashful-Khafa, 2/265)

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