Tosefta for Sotah 8:2

Twice he goes out and speaks with them: Once at the border, and once about the regulations of war. That which is on the border, what does he say? "Go forth and hearken to the words of the [anointed] priest." That which is about the regulations of war, what does he say (Deut. 20:5)? "Who is the man who has built a new house and did not inaugurate it? Let him go forth and return to his home." [If] his house it fell down and he built it [again], behold, that one returns. Rabbi Yehuda says, if he added anything new to it, he returns, and if not, he does not return. Rabbi Eliezer says, the people of Sharon did not have to return to their homes because they renovate them one time every sabbatical cycle.

There are those who go out and return, who go out and do not return, and there are those who do not go out at all. All those about whom they said "They go out and return," they pay city taxes, and they provide water and food for the battle, and they repair the roads. All the rest are those who do not return. All those about whom they said "They do not go out at all": [If] he builds a house and inaugurates it but twelve months did not pass, he planted a vineyard and deconsecrated it but twelve months did not pass, [or] he betrothed a woman and took her [as a wife] but twelve months did not pass, these do not pay city taxes, and they do not provide water and food for the battle, and they do not repair the roads. Rabbi Yehuda would designate an optional war as a "war of mitzvah," but for an obligatory war, everyone goes out, even a bridegroom from his chamber and a bride from her wedding canopy.