The Prophet ﷺ said, "Whoever defends the honor of his brother against backbiting, it becomes a right upon Allah to free him from the Fire."
عن النبي ﷺ قال: من ذب عن لحم أخيه بالغيبة كان حقا على الله أن يعتقه من النار.
Abdullah bin Mubarak reported it in Zuhd (687), and from his route Ahmad (27609) and Tabarani in Kabir (24/176) reported it from Ubaydullah bin Abu Ziyad, from Shahr bin Hawshab, from Asma bint Yazid, and she mentioned it. Its isnad is hasan because of Ubaydullah bin Abu Ziyad Qaddah, who is fine, as Ahmad said, and Ibn Adi said, "Trustworthy narrators have reported from him, and I have not seen anything objectionable in his hadith." I say, there is nothing in his hadith that can be criticized.As for Shahr bin Hawshab, although there is disagreement about him, it is possible that he made an error, attributing it once to the musnad of Abu Darda and another time to the musnad of Asma bint Yazid. It is also possible that he heard it from both of them.