The 'Sancta Mater' is one stanza from the 'Stabat Mater,' a hymn honoring the sorrows of Our Lady.
The Stabat Mater remains a popular hymn in honor of Our Lady of Sorrows, and one stanza in that hymn can also be a brief prayer.
It is called the Sancta Mater, and meditates on the Sorrows of the Virgin Mary.
According to the Raccolta, “Pope Pius VII., by a Brief of Dec. 1, 1815, in order to augment in all the faithful devotion towards the sorrows of most holy Mary, and the more to excite in them grateful recollections of the Passion of her Son, Jesus,” encouraged the faithful to recite the following stanza 7 times, in honor of the 7 Sorrows of Mary.
Holy Mother, pierce me through;
In my heart each wound renew
Of my Savior crucified.