The 9th Schedule to the Constitution of India was added by the :

The Ninth Schedule was added to the Constitution of India by the First Amendment Act, 1951 [2]. This amendment was introduced to protect land reform laws and other legislations from being challenged in courts on the grounds of violating Fundamental Rights [2]. Specifically, it was inserted alongside Article 31B to provide a 'protective umbrella' for laws included within it, shielding them from judicial review [2]. While the original Constitution contained only eight schedules, the First Amendment initiated the expansion of these schedules to address socio-economic development and the abolition of the zamindari system [2]. Although the Fourth Amendment Act of 1955 later added more laws to this schedule, the schedule itself was established by the First Amendment in 1951.

Sources

1. [2] https://repository.nls.ac.in/cgi/viewcontent.cgi?article=1134&context=nlsir