Praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The general narrations prohibiting backbiting represent the evidence provided by scholars to show that it is forbidden for spouses to speak ill of each other after divorce. The sanctity of a Muslim must be honored at all times and speaking ill of him/her before others is part of the prohibited speech. However, this excludes matters for which there is a sound reason in Sharia, such as warding off injustice, complaining to a judge or reacting, to an injury, correspondingly. Allah the Almighty says, "God loveth not that evil should be noised abroad in public speech, except where injustice hath been done; for God is He who heareth and knoweth all things." {An-Nisa`, 148}.
In addition, bringing up the past causes pity and regret, brings evil and gives room for people to backbite them and think ill of them. However, if the couple put the past behind them and each engages in what is beneficial to him/her in this life and the next, this is better and is rewarded by Allah the Almighty. Allah says {What means}: " The recompense for an injury is an injury equal thereto (in degree): but if a person forgives and makes reconciliation, his reward is due from God: for (God) loveth not those who do wrong." {Ash-Shura, 40}. He also says: "But indeed if any show patience and forgive, that would truly be an exercise of courageous will and resolution in the conduct of affairs." {Ash-Shura, 43}.
Narrated Aisha, Ummul Mu'minin: Ata' said: The quilt of Aisha was stolen. She began to curse the person who had stolen it. The Prophet (PBUH) began to tell her: Do not lighten him.
Abu Dawud said: The meaning of the Arabic words la tasbikhi 'anhu means "do not lessen him or lighten him". {Related by Abu Dawoud}.
Moreover, there is a special prohibition for uncovering marital secrets without a reason approved by Sharia. This indicated by the following Hadith: “The most serious breach of trust in God’s sight on the day of resurrection ...” A version has, “Among those who will have the worst position in God’s sight on the day of resurrection is the man who has intercourse with his wife, and she with him, and then spreads her secret.”* * i.e. talks about the subject to others, or tells people about defects or beauties he has found in her. { Related by Muslim}.
An-Nawawi (May Allah be pleased with him) says: "This Hadith prohibits a man from spreading the secrets of the intimate relationship with his wife and telling people about the details of what happens in the bedroom." {Shareh Muslim, vol.80/pp.10}.
In conclusion, it is prohibited to reveal secrets of the spouses or state their defects, whether during marriage or after divorce, except for a considerable benefit stipulated in Sharia, such as giving advice, appealing to a judge or a Mufti. And Allah the Almighty Knowes Best.