Sa'id bin Jubayr narrates from Ibn Abbas (may Allah be pleased with them both): "The Messenger of Allah (peace and blessings be upon him) prayed Zuhr and Asr together, and likewise Maghrib and Isha, without any fear or journey." Imam Malik (may Allah have mercy on him) said: My view is that he did this because of rain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5543