It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) combined the Zuhr and Asr prayers, and the Maghrib and Isha prayers, in Madinah without any excuse. Ibn Abbas (may Allah be pleased with them both) was asked: "What did he (peace and blessings be upon him) intend by that?" He said: "To make things easy for his Ummah."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12590