Praise be to Allah.
Allah, may He be exalted, has mentioned women who are forbidden in marriage because of kinship. Allah says (interpretation of the meaning):
“Forbidden to you (for marriage) are: your mothers, your daughters, your sisters, your father's sisters, your mother's sisters, your brother's daughters, your sister's daughters…”
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
These are seven who are forbidden in marriage, according to the text and scholarly consensus; none of the scholars differed concerning this. End quote from al-Sharh al-Mumti‘, 12/53.
1.The mother, which includes grandmothers on both the father’s and mother’s side
2.The daughter, which includes granddaughters
3.Sisters, whether full sisters or half-sisters through the father or mother
4.The paternal aunt, which also includes the paternal aunt of the father or mother
5.The maternal aunt, which also includes the maternal aunt of the father or mother
6.The brother’s daughter, which includes his granddaughters
7.The sister’s daughter, which includes her granddaughters
Any other women who are relatives, apart from these, are permissible for marriage. Hence Allah, may He be exalted, says in the following verse (interpretation of the meaning): “All others are lawful…” [al-Nisa’ 4:24].
Based on that, the daughter of one’s paternal uncle or aunt, or of one’s maternal uncle or aunt, are permissible in marriage. The Qur’aan states that in the verse (interpretation of the meaning):
“O Prophet (Muhammad SAW)! Verily, We have made lawful to you your wives, to whom you have paid their Mahr (bridal money given by the husband to his wife at the time of marriage), and those (slaves) whom your right hand possesses - whom Allâh has given to you, and the daughters of your ‘Amm (paternal uncles) and the daughters of your ‘Ammaat (paternal aunts) and the daughters of your Khaal (maternal uncles) and the daughters of your Khaalaat (maternal aunts)…”
Based on this, it is permissible for a girl to marry her father’s paternal cousin, because a person’s paternal uncle is an uncle to him and to all his offspring. So her father’s paternal uncle is also an uncle to her, and his son is her cousin, and it is permissible for a girl to marry her paternal cousin.
And it is permissible for your daughter to marry the son of your mother-in-law’s brother, because the brother of your mother-in-law is her maternal uncle, because he is the maternal uncle of her father, and the maternal uncle of one’s father is also an uncle to his children. And it is permissible for a girl to marry her maternal cousin.
And Allah knows best.