Muhammad Ibn Muhammad Al-Mufid writes:

فربسها (فاطمة) برجله (عمر) وكانت حاملة بابن اسمه المحسن فأسقطت المحسن من بطنها

“So he (Umar) kicked her (Fatimah) with his leg when she was pregnant with her son named Muhsin (a.), whereupon she lost him from her womb.” [Al-Ikhtisas, page 183]