Reciting "rabbigh fir li" between the both sajdahs

In regards to saying dua between two sajood during prayer; I contacted local Mufti and received fatwa that reading dua between two sajoods during prayer (Rabigh Firlee) is against the Sunaha of Prophet (Sallallahu Alayhi Wasallam); so there is no need for sajada-e-Sahu if someone don't read dua between two sajoods. I am 35 years old and never read Rabigh Firlee between two sajoods but during Hajj last year; I read in a book that of someone don't say "Rabigh Firlee" between two sajoods then he has to perform Sajad-e- Sahu and since then I am saying this dua between two sajoods. But after I contacted local Mufti for authenticity of this dua; he advised that it is against Sunnah. Please clarify.