8 §1. A plenary indulgence is granted to the Christian faithful who:
2° in any Friday in the season of Lent piously recite the prayer En ego, o bone et dulcissime Iesu, before an image of the Crucified Jesus Christ after communion; ...(Reference: Enchiridion Indulgentiarum, 4th edition, al. concessiones.)
. . .
The En ego is quite well known - it is published in Breviaries and Missals, as well as in all missals for the use of the lay faithful, usually in the section dedicated to thanksgiving after Mass:
En ego, o bone et dulcissime Iesu, ante conspectum tuum genibus me provolvo, ac maximo animi ardore te oro atque obtestor, ut meum in cor vividos fidei, spei et caritatis sensus, atque veram peccatorum meorum paenitentiam, eaque emendandi firmissimam voluntatem velis imprimere; dum magno animi affectu et dolore tua quinque vulnera mecum ipse considero, ac mente contemplor, illud prae oculis habens, quod iam in ore ponebat tuo David Propheta de te, o bone Iesu: «Foderunt manus meas et pedes meos; dinumeraverunt omnia ossa mea». (Behold, o good and most sweet Jesus, I fall upon my knees before Thee, and with most fervent desire beg and beseech Thee that Thou wouldst impress upon my heart a lively sense of faith, hope and charity, true repentance for my sins, and a firm resolve to make amends. And with deep affection and grief, I reflect upon Thy five wounds, having before my eyes that which Thy prophet David spoke about Thee, o good Jesus: "They have pierced my hands and feet, they have counted all my bones.")