Answer
(Fatwa: 750/B=144/tb=1431)
Backbiting is haram and unlawful in the light of the following ayah:
وَلَا يَغْتَب بَّعْضُكُم بَعْضاً أَيُحِبُّ أَحَدُكُمْ أَن يَأْكُلَ لَحْمَ أَخِيهِ مَيْتاً فَكَرِهْتُمُوهُ [الحجرات : 12]
But at some places it is not a sin i.e. backbiting of a debauched person in front of people in order to protect people from his wickedness or to disclose his shortcomings for his reform in front of any pious or great person only as much required or backbiting any Muslim when any religious benefit is attached to it, is not then a sin i.e. the investigation of Imams regarding memorizing Hadith does not fall under the category of backbiting at all.
قال في الدر: إذا كان الرجل يصوم و يصلي و يضر الناس بيده و لسانه فذكره بما فيه ليس بغيبةٍ حتى لو أخبر السلطان بذلك ليزجره لا إثم عليه (درمختار مع الشامى:9/585 ، كتاب الحظر والإباحة).
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband