Just to be clear, purgatory and Abraham’s bosom (or Limbus Patrum) are seperate ‘places’ or ‘states’.
The righteous who had died before Christ awaited His coming in Limbus Patrum, or Abraham’s Bosom.
They endured cleansing in purgatory prior to this ‘place’ and were prepared for Heaven when Christ opened the Gates.
It is principally on the strength of these Scriptural texts, harmonized with the general doctrine of the Fall and Redemption of mankind, **that Catholic tradition has defended the existence of the limbus patrum as a temporary state or place of happiness distinct from **Purgatory. As a result of the Fall, Heaven was closed against men. Actual possession of the beatific vision was postponed, even for those already purified from sin, until the Redemption should have been historically completed by Christ’s visible ascendancy into Heaven. Consequently, the just who had lived under the Old Dispensation, and who, either at death or after a course of purgatorial discipline, had attained the perfect holiness required for entrance into glory, were obliged to await the coming of the Incarnate Son of God and the full accomplishment of His visible earthly mission. Meanwhile they were “in prison,” as St. Peter says; but, as Christ’s own words to the penitent thief and in the parable of Lazarus clearly imply, their condition was one of happiness, notwithstanding the postponement of the higher bliss to which they looked forward. And this, substantially, is all that Catholic tradition teaches regarding the limbus patrum.
Catholic Encyclopedia- Limbo