Muwatta Malik 1816

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

Reference

Muwatta Malik 1816

In-book

Book 56, Hadith 6