I heard the Messenger of Allah ﷺ say: you will make a secure peace with the Byzantines, then you and they will fight an enemy behind you, and you will be victorious, take booty, and be safe. You will then return and alight in a meadow with mounds and one of the Christians will raise the cross and say: The cross has conquered. One of the Muslims will become angry and smash it, and the Byzantines will act treacherously and prepare for the battle. (Using translation from Abū Dāʾūd 4292)
أَنَّهُ قَالَ لَهُ انْطَلِقْ بِنَا إِلَى ذِي مَخْبَرٍ رَجُلٌ مِنْ أَصْحَابِ رَسُولِ اللهِ ﷺ قَالَ فَأَتَيْنَاهُ فَقَالَ سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ سَيُصَالِحُكُمُ الرُّومُ صُلْحًا آمِنًا ثُمَّ تَغْزُونَ أَنْتُمْ وَهُمْ عَدُوًّا فَتُنْصَرُونَ وَتَسْلَمُونَ وَتَغْنَمُونَ ثُمَّ تَنْصَرِفُونَ فَتَنْزِلُونَ بِمَرْجٍ ذِي تُلُولٍ فَيَرْفَعُ رَجُلٌ مِنَ النَّصْرَانِيَّةِ الصَّلِيبَ فَيَقُولُ غَلَبَ الصَّلِيبُ فَيَغْضَبُ رَجُلٌ مِنَ الْمُسْلِمِينَ فَيَقُومُ إِلَيْهِ فَيَدُقُّهُ فَعِنْدَ ذَلِكَ تَغْضَبُ الرُّومُ وَيَجْمَعُونَ لِلْمَلْحَمَةِ