5194 — Qutaybah ibn Sa‘īd narrated to us, al-Layth narrated to us, from Yazīd ibn Abī Ḥabīb, from Abū al-Khayr, from ‘Abd Allāh ibn ‘Amr: that a man asked the Messenger of Allah, peace and blessings be upon him: "Which aspect of Islam is best?" He said: "Feed the food, and greet with salām those you know and those you do not know." (1)

143 — Chapter: How is the salām (greeting)?

5195 — Muḥammad ibn Kathīr narrated to us, Ja‘far ibn Sulaymān informed us, from ‘Awf al-A‘rābī, from Abū Rajā’, from ‘Imrān ibn Ḥuṣayn, who said: A man came to the Prophet, peace and blessings be upon him, and said: "Al-salāmu ‘alaykum" (Peace be upon you). He returned the greeting, then the man sat down. The Prophet, peace and blessings be upon him, said: "Ten." Then another man came and said: "Al-salāmu ‘alaykum wa raḥmatu Allāh" (Peace be upon you and the mercy of Allah). He returned the greeting, and the man sat down. He said: "Twenty." Then another man came and said: "Al-salāmu ‘alaykum wa raḥmatu Allāh wa barakātuh" (Peace be upon you, the mercy of Allah, and His blessings). He returned the greeting, and the man sat down. He said: "Thirty." (2)

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(1) Its chain of transmission is authentic. Al-Layth: he is Ibn Sa‘d al-Miṣrī, and Abū al-Khayr: he is Mirthad ibn ‘Abd Allāh al-Yazanī.
It was also recorded by al-Bukhārī (28), Muslim (39), and al-Nasā’ī in "Al-Mujtabā" (5000) from Qutaybah ibn Sa‘īd, with this chain.
It was also recorded by al-Bukhārī (12) and (6236), Muslim (39), and Ibn Mājah (3253) via other routes from al-Layth, with this chain.
It appears in "Musnad Aḥmad" (6581) and "Ṣaḥīḥ Ibn Ḥibbān" (505).

(2) Its chain is strong. Ja‘far ibn Sulaymān — who is al-Ḍubā‘ī — is truthful and good in hadith.
Muḥammad ibn Kathīr: he is al-‘Abdī, and ‘Awf al-A‘rābī: he is Ibn Abī Jamīlah, and Abū Rajā’: he is ‘Imrān ibn Milḥān.