The actor played the role of a reluctant groom in the '90s Hardiwar in the Sharat Katariya-directed movie.
"Will cherish this for life. Hail Bachchan Saab," Ayushmann tweeted with an Instagram photo of the note.
"Even if I had not met you at the HT style awards, this note would have still been on its way to tell you how greatly I enjoyed your performance in 'Dum Laga Ke Haisha'," Bachchan wrote in the note.
The 72-year-old actor, who was born in Allahabad, said he could not find any mistake in Ayushmann's recreation of the body language and gestures of that place.
