Al-Matalib al-'Aliyah 2686 — Whose name to begin a letter with

It is narrated from Muhammad bin Sirin (may Allah have mercy on him) that Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) wrote a letter to Amir bin Abdullah, whose content was this: "From Abdullah bin Qays (Abu Musa al-Ash'ari) to Amir bin Abdullah, who is called Ibn Abd Qays. To proceed: If your state (of abstinence, piety and former righteous conduct) has changed, then return to your original state; and if you have not changed (but remain firm upon goodness), then persevere in it. And peace be upon you."
[Ibn Abi Shaybah recorded it in al-Musannaf: 34327, and Hannad bin al-Sari in al-Zuhd: 472, and its chain is sahih (authentic).]