Kautilya's Arthashastra 3.4.37

3.4.37

dīrghapravāsinaḥ pravrajitasya pretasya vā bhāryā sapta tīrthāny ākāṅkṣeta, saṃvatsaraṃ prajātā //

In the case of husbands who have long gone abroad (dirgrhapravásinah), who have become ascetics, or who have been dead, their wives, having no issue, shall wait for them for the period of seven menses; but if they have given birth to children, they shall wait for a year. Then (each of these women) may marry the brother of her husband. If there are a number of brothers to her lost husband, she shall marry such a one of them as is next in age to her former husband, or as is virtuous and is capable of protecting her, or one who is the youngest and unmarried. If there are no brothers to her lost husband, she may marry one who belongs to the same gotra as her husband's or relative. But if there are many such persons as can be selected in marriage, she shall choose one who is a nearer relation of her lost husband.