From Adomnán’s Life of St. Columba. May we all have copy-editors this good:

One day Baithéne came to St. Columba and said:

“I need one of the brethren to help me go through the text of the psalter I have copied and correct any mistakes.”

The saint said to him:

“Why do you bring this trouble on us when there is no need? For in your copy of the psalter there is no mistake – neither one letter too many nor one too few – except that in one place the letter I is missing.”

So it was. Having gone through the whole psalter, it was found to be exactly as the saint predicted.