Ek Dil Sau Afsane

Ek Dil Sao Afsane is a Hindi romantic film, made in 1963 directed by R.C. Talwar with Raj Kapoor and Waheeda Rehman in the lead roles.

All the songs picturized on Raj Kapoor was sung by Mukesh,whom Raj Kapoor used as his Singing voice,Except one SongTum Hi Tum ho.It happened one day that Mukesh was unavailable for a Song recording,So Mohammed Rafi was called for a Dubbing Version of the song.Raj Kapoor was So impressed that he used this Dubbed song of Mohammed Rafi in the Film.After hearing the song,Mukesh too quoted that,the way Mohammed Rafi has sung,He couldnt have rendered in that beautiful and melodious way.

Source: Wikipedia