Accepting money from kaafirs

1 – There is no reason why you should not take from the money that your wife has inherited, on condition that that should be with her consent. 

Allaah says (interpretation of the meaning): 

“but if they, of their own good pleasure, remit any part of it to you, take it, and enjoy it without fear of any harm (as Allaah has made it lawful).”

[al-Nisa’ 4:4]

Al-Qurtubi (may Allaah have mercy on him) said: 

The phrase “but if they, of their own good pleasure, remit any part of it to you, take it, and enjoy it without fear of any harm” is addressed to husbands, and indicates that it is permissible for a woman to give her mahr as a gift to her husband, whether she was a virgin or previously married. This is the opinion of the majority of fuqaha’… The scholars are agreed that if a woman who is in control of her own affairs gives her mahr to her husband, that is a valid transaction and she cannot take it back.  

Tafseer al-Qurtubi, 5/24, 25 

In general, if a kaafir gives something to a Muslim “of his own good pleasure”, there is nothing wrong with accepting it. 

The Prophet (peace and blessings of Allaah be upon him) ate with the Jews. (Narrated by al-Bukhaari, 2424; Muslim, 4060) 

The king of Aylah – a land on the seacoast – who was a kaafir, gave him a gift of a white mule and a cloak. (Narrated by al-Bukhaari, 1411; Muslim, 1392). 

The Negus paid the mahr of Umm Habeebah on his behalf, and he was a kaafir. 

It was narrated from Umm Habeebah that the Messenger of Allaah (peace and blessings of Allaah be upon him) proposed marriage to her when she was in the land of Ethiopia. The Negus married her to the Prophet (peace and blessings of Allaah be upon him), giving her on his behalf her a mahr of four thousand dirhams, and prepared her trousseau, and he sent her (to the Prophet (peace and blessings of Allaah be upon him)) with Shurahbeel ibn Hasanah. The Messenger of Allaah (peace and blessings of Allaah be upon him) did not send anything to her. The mahr of his wives was four hundred dirhams. 

(Narrated by al-Nasaa’i, 3350; Abu Dawood, 2086; al-Haakim, 2/181. al-Haakim classed it as saheeh and al-Dhahabi agreed with him). 

And there are many other similar incidents. 

2 – If she wills her possessions to you, and she was following her own religion before she died, it is also permissible for you to take these possessions, because a will is different from inheritance. But if she did not make a will and died, then it is not permissible for you to inherit anything from her. The Prophet (peace and blessings of Allaah be upon him) said: “The Muslim does not inherit from a kaafir and the kaafir does not inherit from a Muslim.” (Narrated by al-Bukhaari, 6383; Muslim, 1614). 

Imam Ibn ‘Abd al-Barr (may Allaah have mercy on him) said: 

It is proven from the narrations of the trustworthy imaams that the Prophet (peace and blessings of Allaah be upon him) said, “The Muslim does not inherit from the kaafir.” So everyone who goes against that, this hadeeth is evidence against him. This is the view of  all the Sahaabah, Taabi’een and fuqaha’ of various regions such as Maalik, al-Layth, al-Thawri, al-Awzaa’i, Abu Haneefah, al-Shaafa’i and all the scholars of hadeeth who spoke on matters of fiqh, that a Muslim should not inherit from a kaafir and a kaafir should not inherit from a Muslim, following this hadeeth. And Allaah is the Source of strength. 

Al-Tamheed, 9/164

And Allaah knows best.