I heard on a catholic radio station an account in the Bible that suggests that we cannot be responsible for what we do not know. Does anyone know this passage?
I’m not sure that’s exactly what they meant. What they were trying to explain, I think, was the concept of invincible ignorance, i.e., that which we never really had a chance to know. Common example: Someone who grew up on a deserted island and never met anyone who could tell him about Jesus.
There is also the concept, though, of culpable ignorance, where someone “could have” known, but as an act of their free will, chose not to know. Those will be held responsible for what they should have known.
God is a just and merciful God. I’m sure there are many passages in the Bible about this. It would, therefore, be unjust for Him to hold anyone accountable for that which they had no way of knowing.
Its called ignorance…
This is certainly Catholic teaching. If we sin through ignorance (eg. “I didn’t know that gossiping was wrong”) then our ignorance can be “vincible”, if we should have known better, or “invicible”, if there was no reasonable way for us to have known better. We are under obligation to be always forming our consciences, through prayer and study, but we are not culpable for what we do not yet know.
From the Catechism of the Catholic Church:
IV. ERRONEOUS JUDGMENT
1790 A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.
**1791 This ignorance can often be imputed to personal responsibility. This is the case when a man "takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin."59 In such cases, the person is culpable for the evil he commits.
1792 Ignorance of Christ and his Gospel, bad example given by others, enslavement to one’s passions, assertion of a mistaken notion of autonomy of conscience, rejection of the Church’s authority and her teaching, lack of conversion and of charity: these can be at the source of errors of judgment in moral conduct.
**1793 If - on the contrary - the ignorance is invincible, or the moral subject is not responsible for his erroneous judgment, the evil committed by the person cannot be imputed to him. It remains no less an evil, a privation, a disorder. One must therefore work to correct the errors of moral conscience.
1794 A good and pure conscience is enlightened by true faith, for charity proceeds at the same time "from a pure heart and a good conscience and sincere faith."60
The more a correct conscience prevails, the more do persons and groups turn aside from blind choice and try to be guided by objective standards of moral conduct.61
However, you have asked specifically for a scripture reference. The Catechism generally cites scripture where it can. I do not know why it has not done so here. The strongest scriptural support I know for this position is John 15:22 “If I had not come and spoken to them, they would have no sin; but as it is they have no excuse for their sin”. There is also James 4:17 “Therefore, to one who knows the right thing to do and does not do it, to him it is sin.” However, neither of these are unequivocal support. Unless someone can find a better scriptural reference, then I think we’ll have to say that this doctrine is more from tradition, and reason (as briefly explained by Scoobyshme above), than directly from scripture. (and hence, the Catholic radio station was incorrect, when they said that it’s in scripture - or possibly you misheard them).
Luke 12:47-48 seems applicable
47* And that servant who knew his master’s will, but did not make ready or act according to his will, shall receive a severe beating. 48 But he who did not know, and did what deserved a beating, shall receive a light beating. Every one to whom much is given, of him will much be required; and of him to whom men commit much they will demand the more.
That is correct. However, continued ignorance is not bliss. It is encumbant on a Catholic to learn what the Church teaches. If a person does not learn the Church teachings through laziness or deliberately refuses to learn then they would be held responsible and culpable for any sin of grave matter they commit.