Ibn Umar received an urgent summons regarding Safiyyah while he was in Makkah, so he set out and continued traveling until the sun set and the stars appeared. He said, "Whenever the Prophet ﷺ was pressed by some urgent matter during a journey, he would combine these two prayers." He then continued on until the twilight disappeared, at which point he stopped and combined the two prayers.
حدثنا سليمان بن داود العتكي حدثنا حماد حدثنا أيوب
أن ابن عمر استصرخ على صفية وهو بمكة فسار حتى غربت الشمس وبدت النجوم فقال إن النبي ﷺ كان إذا عجل به أمر في سفر جمع بين هاتين الصلاتين فسار حتى غاب الشفق فنزل فجمع بينهما
[Its chain of transmission is sahih] Bayhaqi narrated it, 3/159, from the hadith of Hammad bin Zayd, with the same wording. Tirmidhi also narrated it in the chapter on Friday, in the section on what has been said about combining the two prayers, hadith no. 555, from the hadith of Nafi, and he said, "Hasan sahih."