Muwatta Malik 1816
موطأ مالك#1816SahihThese are the words of a Companion, not of the Prophet ﷺ. The chain is graded on its own terms.
وَحَدَّثَنِي مَالِكٌ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ أَبِي صَالِحٍ السَّمَّانِ، أَنَّهُ أَخْبَرَهُ أَنَّ أَبَا هُرَيْرَةَ قَالَ إِنَّ الرَّجُلَ لَيَتَكَلَّمُ بِالْكَلِمَةِ مَا يُلْقِي لَهَا بَالاً يَهْوِي بِهَا فِي نَارِ جَهَنَّمَ وَإِنَّ الرَّجُلَ لَيَتَكَلَّمُ بِالْكَلَمَةِ مَا يُلْقِي لَهَا بَالاً يَرْفَعُهُ اللَّهُ بِهَا فِي الْجَنَّةِ .
Malik related to me from Abdullah ibn Dinar that Abu Salih as- Samman informed him that Abu Hurayra said, "Truly a man utters words to which he attaches no importance, and by them he falls into the fire of Jahannam, and truly a man utters words to which he attaches no importance, and by them Allah raises him into the Garden
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 56:6