(Ahsaab) 33 : 49
يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا نَكَحْتُمُ الْمُؤْمِنَاتِ ثُمَّ طَلَّقْتُمُوهُنَّ مِنْ قَبْلِ أَنْ تَمَسُّوهُنَّ فَمَا لَكُمْ عَلَيْهِنَّ مِنْ عِدَّةٍ تَعْتَدُّونَهَا ۖ فَمَتِّعُوهُنَّ وَسَرِّحُوهُنَّ سَرَاحًا جَمِيلًا
Oh you who believed! If you marry a believing woman and you divorce them before you have touched them, they have no obligation to keep the waiting period you are calculating, and you give them sustenance, and you release them with a beautiful release.
Before you have touched them means before you have engaged in intercourse with them. In such a case there is no need to calculate the waiting period which means she does not have to observe ‘idda’. See explanation 2: 228-230, 236-237.