Question Summary:
What happens on the Day of Judgment if a Muslim wrongs a non-Muslim and how does one seek forgiveness for backbiting others?

Question Detail:

Asalamualaikum Mufti Sohail ibn Arif,
Final questions regarding gheebat.
We know from this Hadith that a Muslim's bad deeds can be deposited in the account of victim (who's being backbited), but does also apply to non-Muslims who're being backbited?
The Hadith is as follows:
The Prophet (salallahu 'alayhi wa sallam) is reported to have said: "Do you know who is bankrupt?" The Companions (radiallahu anhum) replied, 'The bankrupt amongst us is the person who has no money or property." The Prophet (salallahu 'alayhi wa sallam) said, "The bankrupt from amongst my Ummah is the one who will come on the Day of Resurrection with a good record of Salah, Sawm and Zakah. But he also had cursed someone, slandered against someone, unlawfully took the property of another, killed someone or beat someone. Then all of these abused persons will receive parts of his (abuser's) Hasanaat. When all of his (abuser's) Hasanaat have been removed from his record after he (abuser) pays back for what he owes, then the aggrieved persons' sins will be transferred to and thrown on him (abuser) and he (abuser) will be thrown into the Fire." (Related by Muslim and Tirmidhi)
 
2) In your view if someone's been backbiting knowingly OR unknowingly there is a chance he may have lost much thawab from this account. Would sincere tawbah reverse this divine transaction? Would the angels on his shoulders prune his deeds, and re-instate his good deeds?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
1.) The general principle is that the oppressed person will receive the good deeds of the oppressor, and when these are finished the oppressor will have to take on the bad deeds of the oppressed as indicated by the hadith you have mentioned in your inquiry.
However, how will retribution be meted out on the Day of Judgment if a Muslim has wronged a non-Muslim? 
First, we know that the Muslim will be brought to account for the injustices he has committed whether the oppressed party is Muslim or non-Muslim.
In Mirqah al-Mafatih, Mulla Ali Qari (may Allah have mercy on him) has commented on the hadith which states that even the hornless sheep will take their revenge from horned sheep. He states, that if this is the case with animals who are not accountable, then just think about how Allah will establish justice in regards to those given intellect [zawil ‘uqul] among the lowly and the noble, the strong and the weak. 
Second, Mawlana Ashraf Ali Thanwi (may Allah have mercy on him) has mentioned a subtle point regarding the severity of usurping the monetary rights of non-Muslims. 
He states that Mawlana Qasim (may Allah have mercy on him) has explained that taking the wealth of a non-Muslim is in one way worse than taking the wealth of a Muslim (and by analogy other wrongs such as backbiting, slandering, etc). 
The reason is, he explained, that the rule is that the good deeds of the oppressor will be given to the oppressed. Now, if the oppressed is a Muslim these good deeds will benefit him. So even though one Muslim wronged another Muslim by usurping his wealth, the former, in one sense, also did the oppressed Muslim a favor by gifting him his good deeds. 
However, when a Muslim oppresses a non-Muslim, then the Muslim oppressor not only loses his good deeds to the non-Muslim, he also does not benefit the non-Muslim in any noticeable way since the latter's abode will still be the Fire. 
One might ask then what is the benefit of these good deeds going into the account of a non-Muslim if his abode will still be the Fire? 
The answer is that there will be reduction [takhfif] in his punishment, although it will be so scant that the he will not realize or feel that reduction. This does not contradict the Quranic injunction: “The punishment will not be lightened for them, nor will they be given respite.” [3:88] because, one, this reduction in punishment will not be felt by the disbeliever, and two, it does not mean that all disbelievers will be punished with the same punishment, rather their levels of punishment will vary according to their kufr, albeit there will be no reduction in the punishment decreed for them at the time of entering the Fire. [i]
2.) The jurists [fuqahah] divide backbiting into two general categories [ii]: 
 
a.) Backbiting that the person who was backbit is unaware of.
 
→ In this case it would be sufficient for the person to seek forgiveness from Allah and sincerely repent from the sin of backbiting. 
 
b.) Backbiting that the person who was backbit became aware of. 
 
→ In this case it would not suffice for the person to only seek forgiveness from Allah, rather he would also have to seek forgiveness from the person whom he backbit as well. (If this person has passed away then you will make lots of istighfar and dua for them until you are content that this person is satisfied with you.) 
 
When seeking forgiveness from the person you have backbit, it is not necessary to provide details like: “I backbit you and said such and such about you,” as this could cause more trouble. Rather, it would be sufficient to say: “Please forgive me for any wrong that I committed against you.” 
 
→ If there are many people that you have backbit and you don't remember them specifically, then too you will make lots of istighfar and dua for them for by using a generic term for them, “O Allah, all those people who I have backbit, please forgive them...” 
 
Mawlana Thanwi (may Allah be pleased with him) has mentioned that it is also necessary to praise that person in front of the very people you had backbit. This is because these people, after listening to your backbiting, will now have a negative opinion of that person. 
 
Therefore, it is necessary that you praise that person in the gathering in which you backbit him. Even if what you said about that person was true, it will still be correct for you to say that you are no longer sure about what you said and you should advise those people not to have a negative opinion about that person. [iii][iv][v][vi]
 
And Allah Ta’āla Knows Best 
Mufti Sohail ibn Arif,
Assistant Mufti, Darul Iftaa
Chicago, USA
Checked and Approved by,
Mufti Ebrahim Desai.
خطبات حكيم الامت، ٧/ ١٤٥ - ١٤٧  [i]
وإذا لم تبلغه يكفيه الندم وإلا شرط بيان كل ما اغتابه به [ii]
قال بعض العلماء: إذا تاب المغتاب قبل وصولها تنفعه توبته بلا استحلال من صاحبه فإن بلغت إليه بعد توبته قيل لا تبطل توبته، بل يغفر الله تعالى لهما جميعا للأول بالتوبة وللثاني لما لحقه من المشقة، وقيل بل توبته معلقة فإن مات الثاني قبل بلوغها إليه فتوبته صحيحة، وإن بلغته فلا بل لا بد من الاستحلال والاستغفار، ولو قال بهتانا فلا بد أيضا أن يرجع إلى من تكلم عندهم ويكذب نفسه وتمامه في تبيين المحارم (قوله وإلا شرط بيان كل ما اغتابه به) أي مع الاستغفار والتوبة والمراد أن يبين له ذلك ويعتذر إليه ليسمح عنه بأن يبالغ في الثناء عليه والتودد إليه ويلازم ذلك حتى يطيب قلبه، وإن لم يطب قلبه كان اعتذاره وتودده حسنة يقابل بها سيئة الغيبة في الآخرة وعليه أن يخلص في الاعتذار، وإلا فهو ذنب آخر ويحتمل أن يبقى لخصمه عليه مطالبة في الآخرة، لأنه لو علم أنه غير مخلص لما رضي به.
رد المحتار، ٦/ ٤١٠ - ٤١١ 
إسلام أور هماري زندغي، مفتي تقي عثماني ٨/ ١٣٥  [iii]
المرجع السابق، ٨/ ١٣٦ [iv]
المرجع السابق، ٨/ ١٣٢  [v]
إصلاحي خطبات - مفتي تقي عثماني ٤/ ٩٤ [vi]