Mishkat al-Masabih 3849
Abu Umama said:
We went out with God’s Messenger on an expedition and when a man came upon a cave containing some water and vegetables he felt inclined to stay in it and withdraw from the world, so he asked God’s Messenger’s permission regarding that, but he replied, “I was not commissioned with Judaism, or Christianity, but with the easy Hanif religion. By Him in whose hand Muhammad's soul is, a morning or an evening expedition in God’s path is better than the world and what it contains, and for one of you to remain in the line of battle is better than his prayers for sixty years.” 

Ahmad transmitted it.
عَن أبي أُمامةَ قَالَ: خَرَجْنَا مَعَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي سَرِيَّةٍ فَمَرَّ رَجُلٌ بِغَارٍ فِيهِ شَيْءٌ مِنْ مَاءٍ وَبَقْلٍ فَحَدَّثَ نَفْسَهُ بِأَنْ يُقِيمَ فِيهِ وَيَتَخَلَّى مِنَ الدُّنْيَا فَاسْتَأْذَنَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي ذَلِكَ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنِّي لَمْ أُبْعَثْ بِالْيَهُودِيَّةِ وَلَا بِالنَّصْرَانِيَّةِ وَلَكَنِّي بُعِثْتُ بِالْحَنِيفِيَّةِ السَّمْحَةِ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ لَغَدْوَةٌ أَوْ رَوْحَةٌ فِي سَبِيلِ اللَّهِ خَيْرٌ مِنَ الدُّنْيَا وَمَا فِيهَا وَلَمَقَامُ أَحَدِكُمْ فِي الصَّفِّ خَيْرٌ مِنْ صَلَاتِهِ سِتِّينَ سَنَةً» . رَوَاهُ أَحْمد