It is narrated from Sayyiduna al-Nu'man bin Bashir (may Allah be pleased with him): the Prophet (peace and blessings be upon him) said: "Whoever does not give thanks for a little does not give thanks for much, and whoever is not grateful to people does not thank Allah Almighty either. Speaking of the blessing of Allah Almighty is gratitude, and abandoning it (that is, not speaking of it) is ingratitude. Staying together is mercy, and division is punishment."
Abdullah recorded it. Abu Abd al-Rahman, who transmitted it from al-Sha'bi, I do not know; its remaining narrators are thiqat (trustworthy).