Musnad Ahmad 30:2634

Waki’ narrated to us, he said: Hisham bin Sa’d narrated to us, from Sa’id bin Abi Hilal, from Ibn Abi Dhubab, from Abu Hurairah, that a man from the companions of the Prophet, peace and blessings of Allah be upon him, passed by a mountain pass in which there was a sweet spring. He said: Its goodness—meaning the pleasantness of the mountain pass—pleased him, so he said: "If only I were to stay here and seclude myself." Then he said: "No, not until I ask the Prophet, peace and blessings of Allah be upon him." So he asked him, and he said: "The standing of one of you—meaning in the way of Allah—is better than the worship of one of you among his family for sixty years. Do you not love that Allah should forgive you and that you should enter Paradise? Strive in the way of Allah. Whoever fights in the way of Allah for the duration of the milking of a she-camel, Paradise becomes mandatory for him."