Bismihi Ta'ala

Wa alaikum salam

Your question is in regards to a traveller following a resident Imam in a prayer that consists of 4 units. Does the traveller have to complete all four, or is it permissible for him to break off from the Jama'ah after completing 2?

Below is an extract from a book on comparative Fiqh:

' The Jurists are unanimous upon the fact that it is permissible for a traveller to follow a resident in prayer........... also (unanimous) upon the fact that when a traveller follows a resident Imam, it is necessary for him to complete the full 4 units.

The evidence for this is: Abdullah Ibn Abbas (Radiyallahu anhuma) was once asked, "What is it with the traveller, he prays 2 individually and 4 when he follows a resident Imam?" Abdullah Ibn Abbas Radiyallahu anhuma replied, "This is from the Sunnah (way of the Prophet)." (Musnad Ahmad)

Nafi' says that when Abdullah Ibn Umar Radiyallahu anhuma would perform as a traveller behind a resident Imam, he would complete the full four, whereas individually he would perform 2. (Sahih Muslim)

Also, The Prophet Sallallahu alaihi wasallam said, "Indeed the Imam has been appointed so he may be followed, do not contradict him."

The above can be found in al-Fiqhul Islami wa adillatuhu, p. 1357-1358, volume 2 by Wahbah Zuhaili

From the above-mentioned it can be concluded that a traveller must complete all four units of the Salaah if he is praying behind a resident Imam according to all the Jurists. There is no difference of opinion regarding this matter.

And Allah knows best.