The Number of Rakaahs to be Performed before the Asr and Isha salaahs

Q: Salaah-596: If the Sunnah Rakaahs before the Asr or Isha salaahs had to be terminated after two Rakaahs when Jamaa'ah commenced, will the Sunnah be fulfilled? Is it Sunnah to perform four Rakaahs before the Asr and Isha salaahs or are two Rakaahs sufficient?

Answer: If the opportunity exists, four Rakaahs ought to be performed. However, if this is not possible for some reason, two Rakaahs may be performed since one is at liberly to perform either two or four Rakaahs. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2