USE YOUR BRAIN

Alice came across a lion and a unicorn in a forest of forgetfulness. The Lion lies every Mondays, Tuesdays and Wednesdays, and the other days he speaks the truth. The unicorn lies on Thursdays, Fridays and Saturdays, and the other days he speaks the truth.

Lion: Yesterday I was lying.

Unicorn: So was I.

Which day did they say that?