Onan knew that the seed wouldn't be his; and it happened, when he went in to his brother's wife, that he spilled it on the ground, lest he should give seed to his brother.
If brothers dwell together, and one of them die, and have no son, the wife of the dead shall not be married outside to a stranger: her husband's brother shall go in to her, and take her to him as wife, and perform the duty of a husband's brother to her.
Moreover Rut the Mo'avite, the wife of Machlon, have I purchased to be my wife, to raise up the name of the dead on his inheritance, that the name of the dead not be cut off from among his brothers, and from the gate of his place: you are witnesses this day.