Is it permissible to conclude a letter with the phrase "with peace"?

There is no objection to concluding a letter with the word "wa'l-salam" as an abbreviation for "wa'l-salamu 'alayk" (peace be upon you) or "wa'l-salamu 'alaykum" (peace be upon you all), though it is more complete and better to mention the full phrase. This practice has been reported in the Sunnah from the Companions and the Tabi'un (followers), as 'Umar (may Allah be pleased with him), 'Umar ibn 'Abd al-'Aziz, and Ziyad ibn Abi Sufyan concluded their letters with it. It is also expected that the sender should begin their letter with a complete and beneficial salutation.