Musnad Ahmad 652:104

Abdullah said: Yahya ibn Abd Rabbih, the freed slave of Banu Hashim, narrated to us, saying: Abu Waki’ narrated to us, from Abu Abd al-Rahman, from al-Sha’bi, from al-Nu’man ibn Bashir, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said—upon these wooden planks, or upon this pulpit: "Whoever does not thank for the little, does not thank for the much. And whoever does not thank the people, does not thank Allah. Speaking of the blessing of Allah is gratitude, and abandoning it is disbelief. The community is a mercy, and division is a punishment." He said: Abu Umamah al-Bahili then said: "You must adhere to the greatest multitude (al-sawad al-a’zam)." A man said: "What is the greatest multitude?" Abu Umamah said: "This verse in Surat al-Nur: {But if you turn away, then upon him is only that which he is burdened with, and upon you is that which you are burdened with} [al-Nur: 54]."