Surat At-Tawbah - سورة التوبة

إِنَّمَا يَسْتَأْذِنُكَ الَّذِينَ لَا يُؤْمِنُونَ بِاللَّهِ وَالْيَوْمِ الْآخِرِ وَارْتَابَتْ قُلُوبُهُمْ فَهُمْ فِي رَيْبِهِمْ يَتَرَدَّدُونَ

Muhsin Khan: It is only those who believe not in Allah and the Last Day and whose hearts are in doubt that ask your leave (to be exempted from Jihad). So in their doubts they waver.