Hadith 17:452
25754. Umar narrated to us, he said: Abdullah ibn Ziyad narrated to us, he said: Asim narrated to us, from al-Sha'bi, who said: Abu Burdah wrote to a man from the people of the dhimma (protected non-Muslims), greeting him. It was said to him: "Why did you greet him?" He said: "He initiated the greeting to me."
حدثنا عمر قال حدثنا عبد الله بن زياد قال حدثنا عاصم عن الشعبي قال كتب أبو بردة إلى رجل من أهل الذمة يسلم عليه فقيل له لم قلت له فقال إنه بدأني بالسلام