Sayyiduna al-Sa'ib bin Yazid al-Kindi (may Allah be pleased with him), the nephew of al-Namir, said: The prayer was made obligatory as two rak'ahs and two rak'ahs; then the prayer of the resident was increased, and the prayer of the traveller was kept as it was.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6646