Technically, a completely free version of all episodes without ads does not exist legally. However, using the YouTube official playlist and Hotstar's free tier together, you can cover roughly 60% of the season for zero rupees.
Because the show is not currently airing on linear TV (except for reruns on Star Utsav), the demand for a has exploded. Iss Pyaar Kya Naam Doon Season 1 All Episodes Free