I have located this Hadith in Al Mu’jamul Awsat and wanted to know the authenticity:
الغيبة اشد من الزنا
Backbiting is worse than adultery
Imam Tabarani (rahimahullah) has recorded this narration as you have stated. However, ‘Allamah Haythami (rahimahullah) has declared a narrator extremely weak.
(Al Mu’jamul Awsat, Hadith: 6586, Majma’uz Zawaid, vol. 8 pg. 91/92)
This narration should be quoted as the statement of Sufyan ibn ‘Uyaynah (rahimahullah) and not as a Hadith of Rasulullah (sallallahu ‘alayhi wa sallam). See here
And Allah Ta’ala Knows best.
Answered by: Moulana Suhail Motala
Approved by: Moulana Muhammad Abasoomar