Thomas Aquinas on Lying (Summa Theologica II-II.110)

Here is a passage from ST (Second part of the second part, question 110):

"As regards the end in view, a lie may be contrary to
charity, through being told with the purpose of
injuring God, and this is always a mortal sin, for it
is opposed to religion; or in order to injure one's
neighbor, in his person, his possessions or his good
name, and this also is a mortal sin, since it is a
mortal sin to injure one's neighbor, and one sins
mortally if one has merely the intention of committing
a mortal sin. But if the end intended be not contrary
to charity, neither will the lie, considered under
this aspect, be a mortal sin, as in the case of a
jocose lie, where some little pleasure is intended, or
in an officious lie, where the good also of one's
neighbor is intended. Accidentally a lie may be
contrary to charity by reason of scandal or any other
injury resulting therefrom: and thus again it will be
a mortal sin, for instance if a man were not deterred
through scandal from lying publicly."