Using one line of a poem as slogan for t-shirt printing

I used one line "Mai Ishq Likhoon, Tum Banaras Samajhna" as a slogan for printing t-shirts that I sell in the market. Later on, one person contacted me claiming that this is a line from a poem written by him which is copyrighted. He further stated that I can't use the line and I need to withdraw all my t-shirts from the market. If I don't do so, he would file a case in court against me. Can he really file a case as I'm using only one line (thought I wasn't aware)? What should I do in this situation?