It is narrated from Sayyidah Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said to her: "Jibreel conveys greetings of peace to you." Sayyidah Aisha (may Allah be pleased with her) replied: «وعلیہ السلام ورحمۃ اللہ».
Hadith Referenceالادب المفرد / كتاب أهل الكتاب / 1116
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه البخاري ، المناقب : 3768 و مسلم : 2447»
Explanation & Benefits
Shaykh Maulana Usman Muneeb
Benefits and Issues: From this, it is understood that conveying greetings of peace (salam) in absentia is permissible, and responding to it is also Sunnah. Its details have already been discussed under Hadith 827, that both the messenger who conveys the greeting and the one who sends the greeting should be given the supplication of peace, that is, “Alaika wa ‘alayhi as-salam” (peace be upon you and upon him).
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 1116