Hadith #6450 (Sahih Muslim)
Book: The Book of Virtue, Enjoining Good Manners, and Joining of the Ties of Kinship
Narrator(s): Umm al-Darda'a أم الدرداء
Grade: Sahih

I heard Allah’s Messenger (ﷺ) as saying: The invoker of curse would neither be witness nor intercessor on the Day of Resurrection.

Source: https://parallelquran.com/hadith/sahih-muslim-6450/

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Hadith #6759 (Sahih Muslim)
Book: The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness
Narrator(s): Umm al-Darda'a أم الدرداء
Grade: Sahih

My husband reported that he heard Allah’s Mes- senger (ﷺ) as saying: He who supplicates for his brother behind his back (in his absence), the Angel commissioned (for carrying supplication to his Lord) says: Amen, and it is for you also.

Source: https://parallelquran.com/hadith/sahih-muslim-6759/