Al-Matalib al-'Aliyah 2651 — Greeting disbelievers with salam

It is narrated from Kurayb (may Allah have mercy on him), the mawla of Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both), that Sayyiduna Ibn Abbas (may Allah be pleased with them both) wrote a letter to a dhimmi (a non-Muslim citizen of the Islamic state) and began it with the greeting of peace (salam). I said to him (expressing surprise): Do you begin with the salam (for a non-Muslim)? He replied: "Indeed, Allah Almighty is al-Salam (the Source of peace and the Giver of peace)."
Imam Musaddad recorded this athar (report) in his Musnad; its chain contains Sharik bin Abdullah al-Qadi, who is saduq (truthful), but because of a defect in his memory this chain is of hasan (good) grade.