Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates that I performed eight rak‘ahs (Dhuhr and ‘Asr) and seven rak‘ahs (Maghrib and ‘Isha) combined with the Prophet (peace and blessings be upon him) in Madinah Munawwarah. I asked, “Why did you do this, O Messenger of Allah?” He replied that the Prophet (peace and blessings be upon him) wanted that his Ummah should not fall into hardship and difficulty. Although the Prophet (peace and blessings be upon him) was residing in Madinah Munawwarah, he was neither in a state of travel nor fear. In the narration of Sufyan, these words are also present: the Prophet (peace and blessings be upon him) was neither in a state of fear nor travel. Sa‘id bin Jubair says that I asked Sayyiduna Ibn Abbas (may Allah be pleased with them both), “Why did the Prophet (peace and blessings be upon him) combine the prayers in this way?” He replied that the Prophet (peace and blessings be upon him) wanted that no person from his Ummah should feel hardship or difficulty. ‘Abdul Jabbar also narrated to us in this manner once.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الفريضة فى السفر / 971