(sic) Abu 'z-Zinad said, "Kharija (ibn Zayd ibn Thabit) used to write on the letter of Zayd when he said the salam, 'Peace be upon you, Amir al-Mu'minin, and the mercy of Allah and His blessings and His forgiveness and the best of His prayers."
Reference: Al-Adab Al-Mufrad 1001b In-book : Book 42, Hadith 38 English translation : Book 42, Hadith 1001
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