It is narrated from Hazrat Nu'man bin Bashir (may Allah be pleased with him) that the Holy Prophet (peace and blessings be upon him) once said from the pulpit: "Whoever does not thank for a little, does not thank for much either. Whoever does not thank people, does not thank Allah either. To mention Allah's blessings and favors is gratitude; to abandon it is disbelief. Unity is mercy, and division is punishment."
Hadith Referenceمسند احمد / تتمہ مُسْنَدِ الْكُوفِيِّينَ / 19350
Hadith Gradingحکم دارالسلام:وهذا إسناد ضعيف، فيه أبو عبدالرحمن لا يعرف، وقوله: ومن لم يشكر الناس لم يشكر الله صحيح لغيره