Musnad Ahmad 30:3655

'Abd al-Malik ibn 'Amr narrated to us, Hisham ibn Sa'd narrated to us, from Sa'id ibn Abi Hilal, from Ibn Abi Dhubab, from Abu Hurairah, that a man from the companions of the Messenger of Allah (may Allah bless him and grant him peace) passed by a mountain pass in which there was a spring of sweet water. Its goodness pleased him, so he said: "If I were to stay in this mountain pass and seclude myself from the people, but I will not do so until I ask the permission of the Messenger of Allah (may Allah bless him and grant him peace)." He mentioned that to the Prophet (may Allah bless him and grant him peace), and he said: "Do not do so, for the standing of one of you in the path of Allah is better than the prayer of sixty years alone. Do you not love that Allah should forgive you and enter you into Paradise? Go forth to fight in the path of Allah. Whoever fights in the path of Allah for the duration of the milking of a she-camel, Paradise becomes mandatory for him."