Is there a Hadith stating that one should recite Surat Al-Fatiha 100 times to seek blessings?

There is no authentic evidence to prove the permissibility of reciting Al-Fatihah 100 times to ask Allah for something. A Muslim should follow the Sunnah and ask Allah by His Names and Attributes, and seek intercession through them, as Allah Almighty said: "And to Allah belong the best names, so invoke Him by them." Surah Al-Fatihah is the greatest surah, and it is permissible to recite it whenever one wishes, without specifying a number or a particular method that is not mentioned in the Sharia.