Feast Of The Immaculate Conception Of The Blessed Virgin Mary - 8 December

 Quoted below, without hyperlinks, is from Learn Religions [1]:

The Immaculate Conception refers to the condition that the Blessed Virgin Mary was free from Original Sin from the very moment of her conception in the womb of her mother, Saint Anne. We celebrate the Nativity of the Blessed Virgin Mary—her birth—on September 8; nine months before that is December 8, the Feast of the Immaculate Conception.

The Blessed Virgin Mary confirms Her Immaculate Conception to Bernadette Soubirous of Lourdes.  Quoted in part below is from The Arlington Catholic Herald [2]:

On March 2, [1858, Our Lady of Lourdes] asked Bernadette to "Go and tell the priests that people are to come here in procession and to build a chapel here." The parish priest of Lourdes wanted to know the lady’s name, and he asked for a miracle: that a rose bush flower in the middle of winter. After school March 3, Bernadette went to the grotto. When she saw the lady, she asked for her name, only to receive a smile.

On March 4, with about eight thousand people present, the lady returned. The rose bush did not bloom, but she did reveal her name: "Que soy era Immaculada Concepciou." "I am the Immaculate Conception." Bernadette did not know this title was assigned to the Blessed Virgin Mary. Four years earlier, in 1854, Pope Pius IX dogmatically declared this a truth of the Catholic faith.

[1] https://www.learnreligions.com/what-is-the-immaculate-conception-542107#:~:text=The%20Immaculate%20Conception%20refers%20to%20the%20condition%20that,December%208%2C%20the%20Feast%20of%20the%20Immaculate%20Conception.

[2] https://www.catholicherald.com/Faith/Your_Faith/_I_am_the_Immaculate_Conception_/#:~:text=%22%20Bernadette%20did%20not%20know%20this%20title%20was,felt%20that%20she%20was%20in%20front%20of%20it.