لَولا جاءوا عَلَيهِ بِأَربَعَةِ شُهَداءَ ۚ فَإِذ لَم يَأتوا بِالشُّهَداءِ فَأُولـٰئِكَ عِندَ اللَّهِ هُمُ الكاذِبونَ

Why did they [who slandered] not produce for it four witnesses? And when they do not produce the witnesses, then it is they, in the sight of Allah, who are the liars.