The Padma Shri recipient bowed out of B-Town in 1993, his last track being "Is Se Jyada Dukh Na Koi" from "Shreemaan Aashique".
"The song is dedicated to God and humanity. I was so touched by the film's subject that I decided to sing the track. It's my tribute to those who lost their lives in 1984 (riots)," Khan said in a statement issued here.
It was writer-producer Harry Sachdeva's determination to convince Khan to sing a song for "31st October" featuring Soha Ali Khan and Vir Das.
The movie is slated to hit the screens on October 7.