We do not have a lot of information about the righteous woman Aasiyah bint Mazaahim, the wife of Pharaoh. All the details that have been narrated about her are from the Israa’eeliyyaat (stories from Jewish sources) and are not proven in any saheeh text as far as we know.
But it seems – and Allaah knows best – that she was one of those who concealed their faith from Pharaoh, then her secret was found out. There follow some of the things that have been narrated about her, with some commentary:
1 – Allaah says (interpretation of the meaning):
“And Allaah has set forth an example for those who believe: the wife of Fir’awn (Pharaoh), when she said: ‘My Lord! Build for me a home with You in Paradise, and save me from Fir’awn (Pharaoh) and his work, and save me from the people who are Zaalimoon (polytheists, wrongdoers and disbelievers in Allaah)’”
2 – It was narrated that Abu Moosa al-Ash’ari said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The men who attain perfection are many, but there are no woman who have attained perfection apart from Aasiyah the wife of Pharaoh and Maryam bint ‘Imraan, and the superiority of ‘Aa’ishah over all other women is like the superiority of thareed over all other foods.”
(Narrated by al-Bukhaari, 3230; Muslim, 2431)
3 – It was narrated that Ibn ‘Abbaas said: the Messenger of Allaah (peace and blessings of Allaah be upon him) drew four lines on the ground, then he said, “Do you know what this is?” We said, “Allaah and His Messenger know best.” The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The best of the women of Paradise are Khadeejah bint Khuwaylid, Faatimah bint Muhammad, Aasiyah bint Mazaahim the wife of Pharaoh, and Maryam bint ‘Imraan – may Allaah be pleased with them.”
(Narrated by Ahmad, 2663. Classed as saheeh by al-Albaani in Saheeh al-Jaami’, 1135)
4 – It was narrated from Anas that the Prophet (peace and blessings of Allaah be upon him) said: “Sufficient for you among the women of the world are Maryam the daughter of ‘Imraan. Khadeejah bint Khuwaylid, Faatimah bint Muhammad and Aasiyah the wife of Pharaoh.”
(Narrated and classed as saheeh by al-Tirmidhi, 3878)
5 – al-Haafiz ibn Hajar said:
Among the virtues of Aasiyah the wife of Pharaoh is that she chose death over royal privilege and torment in this world over the luxury in which she was living. And her insight concerning Moosa (peace be upon him) was correct when she said “A comfort of the eye for me” [al-Qasas 28:9 – interpretation of the meaning].
Fath al-Baari, 6/448
And Allaah knows best.