Doubts which make prayers void

1174. The following doubts make prayers void:

1. Doubts about the number of Rak’ats occurring in obligatory prayers which consist of 2 Rak’ats, like, Fajr prayers, or prayers offered by a traveler. However, doubt about number of Rak’ats in Mustahab prayers or Namaz of Ihteyat does not make the prayers void.
2. Doubts about the number of Rak’ats occurring in prayers consisting of 3 Rak’ats (like, Maghrib prayers).