Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
quran:9:45

Only those would ask permission of you who do not believe in Allah and the Last Day and whose hearts have doubted, and they, in their doubt, are hesitating.  

They alone ask leave of you, to stay behind, who do not believe in God and the Last Day, and whose hearts are doubtful, uncertain, about religion, so in their doubt they waver, they are confused.
القرآن:٩:٤٥

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

{إنما يستأذنك} في التخلُّف {الذين لا يؤمنون بالله واليوم الآخر وارتابت} شكت {قلوبهم} في الدين {فهم في ريبهم يترددون} يتحيرون.