The full Hadith is as follows:
Sayyiduna Nu’man ibn Bashir (radiyallahu ‘anhu) reported, Rasulullah (sallallahu ‘alayhi wa sallam) said upon the mimbar: “Whoever is not grateful for small things will not be grateful for large things. Whoever is not grateful to people is not thankful to Allah. Mentioning the blessing of Allah is gratitude and not doing so is ingratitude. Unity is a mercy and division [of hearts] is a punishment”
(Musnad Ahmad; Zawaid ‘Abdullah ibn Imam Ahmad, vol. 4 pg. 278 and vol. 4 pg. 375)
Allamah Mundhiri (rahimahullah) has declared the chain sound.
(Targhib, vol.2 pg.78)
And Allah Ta’ala Knows best.
Answered by: Moulana Suhail Motala
Approved by: Moulana Muhammad Abasoomar
Checked by: Moulana Haroon Abasoomar