It is narrated from Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) that he wrote a letter to a dihqan (a non-Muslim Persian landowner) and wrote a salam to him in his letter. He was asked (by way of objection): "Are you writing a salam to him even though he is a disbeliever?" He replied: "He wrote a letter to me in which he greeted me with salam, so I have (in reply) returned his greeting."
[Ibn Abi Shaybah recorded it in al-Musannaf: 26343, and its chain is sahih.]
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الأدب / 2653
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :إسناده صحيح. » «انفرد به المصنف من هذا الطريق»