This was the first Hindi ghost film to have a song which works as a leitmotif through out the film. This became a trend and was followed in other suspense/ghost films such as Madhumati, Woh Kaun Thi and Mera Saaya.
The Song "Aayega Aanewala" was the first Hit Song of Lata Mangeshkar. During that period, songs would be attached to the characters of the Movie and people would not get to know the Singer. This song became that when AIR (All India Radio) played it, people called up to know the name of the singer, and AIR subsequently called up the Recording House to know. Today, Lata Mangeshkar is the undisputed female playback singing queen of India.
During the recording of the film music, a man carelessly said that if the film didn't prove to be a hit it would be because of the music. When the film was released, however, the music was extremely popular, and music director Khemchand Prakash received letters from all over India. Even though he was ill at the time, Prakash went to that man's house and made him read all those letters.
The song "ayega aanewala" wala was latter used in Vishesh Film's movie "Khamoshiyan". The production house purchased rights if the song for its 2015 release as Mahesh Bhatt thought that no other song could go well with the mood of the movie other than this hit number from a Mahal in magical voice of Lata ji.
One example that comes to my mind where the Hindi song definitely came first is a song by the British 1960s-era folk-rock band "The Incredible String Band"... the song is called "White Bird" and is on their album "Changing Horses" - the main theme of the refrain is clearly borrowed from the song "Ayegaa Aane Wala" from Mahal. Since Mahal came out in 1949, when the members of The Incredible String Band would still have been infants, it's pretty clear which direction the borrowing was in. Sorry if this has been mentioned before.
In those days there was system of mentioning the singer's name on the records. This system came after Lata Mangeshkar fought for this. Then the singer's who sang for the film would get mentioned in the credit tittles of the film and on records