Halakhah su Genesi 50:28

From the laws of the commandment is that which they, may their memory be blessed, said (Rif, Ramban and Rashba on Moed Katan 14b) that the first day is by Torah writ and the [next] six are rabbinic. And even though it is stated (Genesis 50:10), "and he made a mourning for his father seven days," [when] the Torah was given, the law was recreated (a new law came into being). And nonetheless they, may their memory be blessed, said (Mishneh Torah, Laws of Mourning 1:1) that Moshe, our teacher, ordained seven days of mourning and seven days of festivity. And they, may their memory be blessed, said (Moed Katan 27a) that the obligation of mourning does not begin until the coffin cover is closed - meaning to say that the whole time that he is not buried, the mourner is not forbidden in anything from all of the things of mourning. And because of this reason, King David bathed and anointed [himself] when [his] child died, before [the child] was buried. And that which they said (Shabbat 136a) that we do not mourn for any [infant] that has not [been alive] for thirty days, is because of a doubt. But they, may their memory be blessed, said in the Gemara that if we clearly know that he has finished his months [of gestation], his law is like the law of other dead people regarding mourning; and likewise for all the other things is his law like a complete person.