Abu Ja’far Ibne Jarir Tabari has narrated through his authorities from Abdullah bin Abbas that he said: We were in the company of Imam Hasan (a) when a butcher passed by with a cow.
Imam (a) said: This cow is pregnant with a female calf having a white spot on its forehead and a white tail.
So we followed the butcher. When he slaughtered the cow the same calf was found inside her as the Imam had foretold.
We said to the Imam: It is the dignity of Almighty Allah to be aware of what is present in the wombs; but how did you gain this knowledge?
Imam Hasan (a) replied: We are aware of this hidden and concealed knowledge which none is aware of except our Prophet and his progeny; not even messenger prophets and proximate angels.
Dalailul Imamah, Pg. 67; Farajul Mahmoom, Pg. 223.