Sifrei Devarim 46

¹(Devarim 11:19) "And you shall teach them to your sons to speak in them": and not to your daughters — whence they ruled: When a child begins to speak, his father should speak to him in the holy tongue and teach him Torah; and if he does not do so, it is as if he had buried him, it being written "And you shall teach them (words of Torah) to your sons to speak in them … (21) so that your days will be multiplied and the days of your sons." And if not, your days will be shortened. For thus are words of Torah expounded: From the negative, you infer the positive; and from the positive, the negative.