It was revealed to Santa Matilde di Hackeborn, a Benedictine nun who died in 1298, as a sure means of obtaining the grace of a good death. Our Lady told her:

If you want to obtain this grace, recite three Hail Marys every day to thank the Blessed Sacrament. These are three privileges of which it has enriched me. With the first, you will thank God the Father for giving me His power, and through it, you will pray that I may be assisted at the hour of death. With the second, you will thank God the Son for sharing His wisdom with me, so that I know the Trinity better than all the saints. For this, you will ask that at the hour of death, your soul may be illuminated with the light of faith and that all ignorance and error be cast away from you. With the third, you will thank the Holy Spirit for filling me with so much love and goodness that, after God, I am the most tender and merciful. For this incomparable goodness, you will ask that at the time of your death, I may fill your soul with the sweetness of divine love and transform the pains of death into sweetness.

At the end of the last century and in the first two decades of the present, the devotion of the Three Hail Mary spread rapidly in various countries of the world for the zeal of a French Capuchin, Fr. Giovanni Battista di Blois, assisted by the missionaries.

It became a universal practice when Leo XIII granted indulgences and prescribed that the Celebrant recite the Three Hail Marys with the people after Holy Mass. This prescription lasted until Vatican Council II.

Pope John XXIII and Paul VI gave a special blessing to those who propagate it.Many Cardinals and Bishops gave impulse to the spread the prayer.

Many Saints were its propagators. Sant ‘Alfonso Maria de’ Liquori, as a preacher, confessor and writer, did not cease to inculcate the good practice. He wanted everyone to adopt it.

St. John Bosco strongly recommended it to his young people. Even the blessed Pio of Pietrelcina was zealous propagator. St. John B. de Rossi, who every day devoted up to ten or twelve hours to the ministry of confessions, attributed to the daily recitation of the Three Hail Mary the conversion of obstinate sinners.

Practice:
Prayerfully pray every day like this:

Mary, Mother of Jesus and my Mother, defend me from the evil one in life and in the hour of death

for the power that the Eternal Father granted you
Ave Maria…

for the Wisdom which the Divine Son granted you.
Ave Maria…

for the Love that the Holy Spirit has given you.
Ave Maria…