حَدَّثَنَا حُسَيْنُ بْنُ مُحَمَّدٍ، حَدَّثَنَا إِسْرَائِيلُ، عَنْ سِمَاكٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ
قَالَ: قَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ كُنْتُ فِي رَكْبٍ أَسِيرُ فِي غَزَاةٍ مَعَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَحَلَفْتُ فَقُلْتُ: لَا وَأَبِي فَهَتَفَ بِي رَجُلٌ مِنْ خَلْفِي لَا تَحْلِفُوا بِآبَائِكُمْ فَالْتَفَتُّ فَإِذَا هُوَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ
Umar (رضي الله عنه) said: I was marching with a group of people on a campaign with the Messenger of Allah (sallallahu alayhi wa sallam), and I swore, saying: No, by my father. A man behind me called out: “Do not swear by your fathers.” I turned around and saw it was the Messenger of Allah (sallallahu alayhi wa sallam).
Musnad Ahmad 276, Book 2, Musnad `Umar b. al-Khattab (ra), Hadith 199. 1 min read