St. Diadochus of Photike
From the Treatise by St. Diadochus of Photike, "On Perfection" (Ch. 14)
"He who has a heartfelt love for God is known by him. For a person grows in the love of God in the measured in which he takes that love into his inmost soul. Which is why, afterwards, such a one passionately longs for the illumination of knowledge to the point of feeling in his very bones, no longer aware of himself but wholly transformed by the love of God. Such a one is in this life without being in it. He still lives in his own body but unceasingly goes out to God through love by the very momentum of his soul. Hence forward, his heart to burning with the fire of love he adheres to God with a sort of irresistible desire, as if quite torn away from the love of self by the love of God."
According to Wikipedia:
"Saint Diadochos of Photiki was a fifth century ascetic whose work is included in the Philokalia. Scholars have acknowledged his great influence on later Byzantine saints such as Maximos the Confessor, John Climacus, Symeon the New Theologian, and in general the Hesychast movement of the 14th century. He has also had great influence in the West via the work, "On the Contemplative Life" (De vita contemplativa) of Julian Pomerius (†498). His feast day is commemorated on March 29. Diadochos was born c. 400 and died sometime before 486. He became bishop of Photiki, a small town in the province of Old Epira, in the northwestern part of present-day Greece. In 451, he took part in the Council of Chalcedon as Bishop of Photiki... His exact date and place of death are thus unknown, although it is assumed he died before 486."