Narrated Suwayd ibn Hanzalah: We went out intending (to visit) the Messenger of Allah (ﷺ) and Wa'il ibn Hujr was with us. His enemy caught him. The people desisted from swearing an oath, but I took an oath that he was my brother. So he left him. We then came to the Messenger of Allah (ﷺ), and I informed him that the people desisted from taking the oath, but I swore that he was my brother. He said: You spoke the truth: A Muslim is a brother of a Muslim.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَمْرُو بْنُ مُحَمَّدٍ النَّاقِدُ، حَدَّثَنَا أَبُو أَحْمَدَ الزُّبَيْرِيُّ، حَدَّثَنَا إِسْرَائِيلُ، عَنْ إِبْرَاهِيمَ بْنِ عَبْدِ الأَعْلَى، عَنْ جَدَّتِهِ، عَنْ أَبِيهَا، سُوَيْدِ بْنِ حَنْظَلَةَ قَالَ خَرَجْنَا نُرِيدُ رَسُولَ اللَّهِ وَمَعَنَا وَائِلُ بْنُ حُجْرٍ فَأَخَذَهُ عَدُوٌّ لَهُ فَتَحَرَّجَ الْقَوْمُ أَنْ يَحْلِفُوا وَحَلَفْتُ أَنَّهُ أَخِي فَخَلَّى سَبِيلَهُ فَأَتَيْنَا رَسُولَ اللَّهِ صلى الله عليه وسلم فَأَخْبَرْتُهُ أَنَّ الْقَوْمَ تَحَرَّجُوا أَنْ يَحْلِفُوا وَحَلَفْتُ أَنَّهُ أَخِي قَالَ " صَدَقْتَ الْمُسْلِمُ أَخُو الْمُسْلِمِ " .
sunnah.com