Al-Kāfi - Volume 2 > Truthfulness and Trust
Hadith #3

3ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ سَهْلِ بْنِ زِيَادٍ عَنِ ابْنِ أَبِي نَجْرَانَ عَنْ مُثَنًّى الْحَنَّاطِ عَنْ مُحَمَّدِ بْنِ مُسْلِمٍ عَنْ أَبِي عَبْدِ الله (عَلَيهِ السَّلام) قَالَ مَنْ صَدَقَ لِسَانُهُ زَكَى عَمَلُهُ.

3. A number of our people have narrated from Sahl ibn Ziyad from ibn abu Najaran from Muthanna al-Hannat from Muhammad ibn Muslim from abu ‘Abd Allah (a.s.) who has said the following: “Abu ‘Abd Allah (a.s.) has said, ‘Whoever’s tongue is truthful; his deeds are clean and pure.’”