Abu Qilabah (may Allah have mercy on him) narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both): When you are travelling and a halting place is not available to you, keep travelling until you reach a halting place where you combine the two prayers. If you have halted and some matter makes you hurry, combine the two prayers, then set off.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5534