Should a traveler pray four rak’ahs with the congregation or pray two rak’ahs on his own?

Prayer in congregation is obligatory for men whether they are at home or traveling. If you find a group of travelers, you should pray ‘Isha’ with them, in the shortened form, otherwise you should pray four rak’ahs in congregation with the people who live there. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: “The obligation to pray in congregation is not waived for the traveler, because Allaah has enjoined it (prayer in congregation) even at the time of battle, as He says (interpretation of the meaning): 

“When you (O Messenger Muhammad) are among them, and lead them in As-Salaah (the prayer), let one party of them stand up [in Salaah (prayer)] with you taking their arms with them; when they finish their prostrations, let them take their positions in the rear and let the other party come up which have not yet prayed, and let them pray with you”

[al-Nisa’ 4:102]

Based on this, if the traveler is in a country other than his own, he has to attend prayer in congregation in the mosque if he hears the adhaan, unless he is far away from the mosque or fears that he will lose his traveling-companions, because of the general meaning of the evidence which indicates that it is obligatory to pray in congregation for the one who hears the adhaan or iqaamah. 

From Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen, vol. 15, question no. 1085. and Allaah knows best.