All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If your mother lived in a place where she could not learn obligatory religious knowledge because of the small number of Muslim scholars in that place, or the inability to reach them, or similar reasons that rule out any negligence to learn the Islamic rulings concerning her job, then what she earned from her Riba (interest and/or usury) work before knowing that it is forbidden, is lawful to her and she does not have to get rid of it. Allaah Says (what means): {…So whoever has received an admonition from his Lord and desists may have what is past, and his affair rests with Allaah.}[Quran 2: 275]
Ibn Katheer interpreted the verse by saying: “So anyone who stopped dealing with Riba as soon as he realized its ruling is given the right of legal ownership of anything he earned prior to this knowledge.” Al-Baydawi added: “…and it is not taken back from him.”
Although this verse is particular to the prohibition of Riba, it also includes those who did not know the ruling of Riba. This is emphasized by the following verse. Allaah Says (what means): {…And We never punish until We have sent a Messenger (to give warning).} [Quran 17: 15] Allaah also Says (what means): {… that I may warn you thereby and whomever it reaches…} [ Quran 6: 19]
Ibn Taymiyyah said: “When the order of the Prophet to do something does not reach someone, it is not obligatory upon him to do that act.”
Shaykh Abdur-Rahmaan Ibn Hassan was asked about an invalid contract in a transaction in Islam, if such transaction has been completed and every member has taken what he wanted, the Shaykh said: “There are three cases as far as the transactions of the Muslim are concerned:
- Sometimes he believes he can solve some problem by following what the more knowledgeable people do, or by acting himself (Ijtihad).
- Other times, he deals ignorantly not knowing that it is Riba.
- Finally, he fulfills a deal knowing that it is pure Riba, which is forbidden.
As for the first and second situation, there are two different opinions about them:
1) If he knows after the completion of the deal that it is Riba, he returns what he has taken just like the person who takes something by force.
2) The second opinion is that he does not return it and this is the most correct one.
But if your mother was in a place where she could have studied the Sharee’ah and she neglected to do so, then she is not excused for her ignorance because the Muslim should learn the rulings of his religion that concern him/her. As a result, her earnings were ill-gotten and she should get rid of them by spending them in the general welfare of the Muslims.
As for the money she got as retirement earnings, if they were originally taken from her salary, then the same ruling above applies to them. So, what was taken from her salary before she knew the ruling is lawful and what was taken after she knew the ruling is unlawful and she has to get rid of it. But if this retirement money was presented as a gift, then she should not take it as it is forbidden for her to do so.
If she had already got hold of this ill-gotten money, then she should get rid of it by spending it in the general benefit of the Muslims, like building hospitals, treating sick people and giving it to the needy and poor people. Whatever she earned from her work, after she knew it was forbidden, is forbidden for her whether while thinking to quit or while working.
As for the degree you received, it is not forbidden if its field is lawful because the prohibition is independent from this certificate itself; it is in your acceptance to have her spend on you from unlawful earning.
Allaah Knows best.