إِذْ تَلَقَّوْنَهُ بِأَلْسِنَتِكُمْ
When you were welcoming it with your tongues - 24:15.
The word تَلَقَّی means to make inquiries from each other (to be inquisitive) and repeat before others. Here it means to repeat hearsay without probe and proof.(1)
وَتَحْسَبُونَهُ هَيِّنًا وَهُوَ عِندَ اللَّـهِ عَظِيمٌ
And were taking it as a trivial matter, while in the sight of Allah it was grave - 24:15.
(1). Lexically the word also means 'welcoming'. This meaning is adopted in the translation of the text, because it also covers the meaning of receiving and conveying the news without hesitation. (Editor)
It means that you regarded it a trifle matter that you heard it and passed it on to others. But in the sight of Allah it was a great sin that without probing and finding out any proof you passed on something to
others to cause harm to other Muslims and to make their life miserable.