In Spiritu Venti
A Message for Sister Faustina: 'I Desire that the First Sunday After the Resurrection be the Feast of Mercy'
The second Sunday of Easter, known today as Divine Mercy Sunday, is not a celebration that arose simply through liturgical development, but rather the fruit of a concrete request from Christ to Sister Faustina Kowalska, which in time was embraced by the entire Church.
Source : Infovaticana