What did the Prophet (saw) order Al-Bara to do when he mentioned the event of slaughtering the animal before the prayer?
      Narrated Al-Bara bin Azib that once he had a guest, so he told his      family (on the Day of Id-ul-Adha) that they should slaughter the      animal for sacrifice before he returned from the ('Id) prayer in order     that their guest could take his meal. So his family slaughtered (the      animal ) before the prayer. Then they mentioned that event to the      Prophet who ordered Al-Bara to slaughter another sacrifice. Al-Bara'      said to the Prophet , "I have a young milch she-goat which is better      than two sheep for slaughtering." (The sub-narrator, Ibn 'Aun used to      say, "I don't know whether the permission (to slaughter a she-goat as      a sacrifice) was especially given to Al-Bara' or if it was in general      for all the Muslims.") (See Hadith No. 99, Vol. 2.)