The Light
إِذْ تَلَقَّوْنَهُۥ بِأَلْسِنَتِكُمْ وَتَقُولُونَ بِأَفْوَاهِكُم مَّا لَيْسَ لَكُم بِهِۦ عِلْمٌ وَتَحْسَبُونَهُۥ هَيِّنًا وَهُوَ عِندَ ٱللَّهِ عَظِيمٌ
When you received it with your tongues and said with your mouths that of which you had no knowledge and thought it was insignificant while it was, in the sight of Allah, tremendous.
Nearby ayahs help place verse 24:15 in sequence and meaning.
لَّوْلَا جَآءُو عَلَيْهِ بِأَرْبَعَةِ شُهَدَآءَ ۚ فَإِذْ لَمْ يَأْتُوا۟ بِٱلشُّهَدَآءِ فَأُو۟لَـٰٓئِكَ عِندَ ٱللَّهِ هُمُ ٱلْكَـٰذِبُونَ
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.
وَلَوْلَا فَضْلُ ٱللَّهِ عَلَيْكُمْ وَرَحْمَتُهُۥ فِى ٱلدُّنْيَا وَٱلْـَٔاخِرَةِ لَمَسَّكُمْ فِى مَآ أَفَضْتُمْ فِيهِ عَذَابٌ عَظِيمٌ
And if it had not been for the favor of Allah upon you and His mercy in this world and the Hereafter, you would have been touched for that [lie] in which you were involved by a great punishment
وَلَوْلَآ إِذْ سَمِعْتُمُوهُ قُلْتُم مَّا يَكُونُ لَنَآ أَن نَّتَكَلَّمَ بِهَـٰذَا سُبْحَـٰنَكَ هَـٰذَا بُهْتَـٰنٌ عَظِيمٌ
And why, when you heard it, did you not say, "It is not for us to speak of this. Exalted are You, [O Allah]; this is a great slander"?
يَعِظُكُمُ ٱللَّهُ أَن تَعُودُوا۟ لِمِثْلِهِۦٓ أَبَدًا إِن كُنتُم مُّؤْمِنِينَ
Allah warns you against returning to the likes of this [conduct], ever, if you should be believers.