Beating female slaves for covering up?

In [Sahih Muslim 1657b](https://sunnah.com/muslim:1657b) it says, > But he (Ibn Umar) said: You are free. He then took hold of something from the earth and said: There is no reward for me even to the weight equal to it. I heard Allah's Messenger (ﷺ) as saying: He who beats a slave **without cognizable offence of his** or slaps him (without any serious fault), then expiation for it is that he should set him free. Now, Musannaf ibn Abi Shaybah 6/236 says > Anas reported: > Umar saw one of our maidservants wearing a veil and he flogged her. Umar said: Do not resemble free women My question is, is wearing a veil really a cognizable offense worth hitting slave girls for?