Abu Mijlaz (may Allah have mercy on him) said: I asked Sayyiduna Ibn Umar (may Allah be pleased with them both): A traveller catches two rak'ahs with the people (that is, with the residents); will the two rak'ahs suffice him, or should he pray the complete prayer as they do? Sayyiduna Ibn Umar (may Allah be pleased with them both) laughed and said: He should pray the complete prayer as they do, that is, he should complete four rak'ahs.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5503