Mujahid (may Allah have mercy on him), concerning this saying of Allah Almighty: "And if you distort or turn away, then indeed Allah is ever aware of what you do" [Surah al-Nisa': 135], says: "If you alter the testimony or conceal it, Allah is aware of what you do."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20591