Layth reported: Mujahid, may Allah have mercy on him, said, “Whoever is safe from two characteristics will secure his fasting: backbiting and falsehood.”
Source: Faḍāʼil al-Awqāt 65
عَنْ لَيْثٍ عَنْ مُجَاهِدٍ رحمه الله قَالَ خَصْلَتَانِ مَنْ حَفِظَهُمَا سَلِمَ لَهُ صَوْمُهُ الْغِيبَةُ وَالْكَذِبُ
65 فضائل الأوقات للبيهقي