Rabi'ah bin Abi Abd al-Rahman said: Abdullah bin Dinar narrated to me, and he was among the righteous, truthful and religious Muslims; he said: The sun set while we were with Sayyiduna Ibn Umar (may Allah be pleased with them both). We kept travelling. When we saw that evening had come, we said: The prayer! He remained silent until the twilight had also disappeared and the stars had shone out. He dismounted and combined the two prayers. Then he said: "I saw the Messenger of Allah (peace and blessings be upon him): when he (peace and blessings be upon him) was in haste on a journey, he would pray these two prayers in this way," that is, he would combine them after night had come.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5518