It did not befit the people of Madina and those around them of the desert Arabs to stay behind (refusing to go with) the messenger of Allah nor to prefer their own lives to his life. That is because there does not afflict them thirst or fatigue or hunger in the way of Allah nor do they tread a path which angers the infidels nor do they receive from their enemy whatever they receive, but a righteous deed is recorded for them thereof. Allah certainly does not waste the reward of the doers of good,
Believers who go out fighting in the cause of Allah (SWT) are rewarded many times more than all the efforts they put in.