From Sahih Muslim (Hadith 1570):
A'isha, the wife of the Messenger of Allah (ﷺ), reported:The prayer was prescribed as two rak'ahs, two rak'ahs both in journey and at the place of residence. The prayer while travelling remained as it was (originally prescribed), but an addition was made in the prayer (observed) at the place of residence
Reference: Muslim 1570