Origen
Catena Aurea · Matthäusevangelium 18
Take heed that ye despise not one of these little ones; for I say unto you, That in heaven their angels do always behold the face of my Father which is in heaven. For the Son of man is come to save that which was lost. How think ye? if a man have an hundred sheep, and one of them be gone astray, doth he not leave the ninety and nine, and goeth into the mountains, and seeketh that which is gone astray? And if so be that he find it, verily I say unto you, he rejoiceth more of that sheep, than of the ninety and nine which went not astray. Even so it is not the will of your Father which is in heaven, that one of these little ones should perish.
Some will have it that an Angel is given as an attendant minister from the time when in the laver of regeneration the infant is born in Christ; for, say they, it is incredible that a holy Angel watches over those who are unbelieving and in error, but in his time of unbelief and sin man is under the Angels of Satan. Others will have it, that those who are foreknown of God, have straightway from their very birth a guardian Angel.