Arabic text
عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ عَنِ النَّبِيِّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَا يَشْكُرُ اللَّهَ مَنْ لَا يَشْكُرُ النَّاسَ»
Translation
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (ﷺ) said: "He who does not thank people in fact does not thank Allah."
Explanation
The Prophet (ﷺ) informed that one who habitually does not thank people for the kindness and good they show him does not truly thank Allah because the two are connected. A person whose nature and habit are to be ungrateful to people and fail to thank them will likewise be inclined to be ungrateful for Allah's blessings and neglect showing gratitude to Him.
Source: HadeethEnc.com