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Abud Darda’ said: While we were with God’s messenger discussing what would come to pass God’s messenger said, “When you hear that a mountain has moved from its place believe it; but when you hear that a man's nature has changed do not believe it, for he will remain true to his inborn disposition.” Ahmad transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَبِي الدَّرْدَاءِ قَالَ بَيْنَمَا نَحْنُ عِنْدَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَتَذَاكَرُ مَا يَكُونُ إِذْ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: إِذَا سَمِعْتُمْ بِجَبَلٍ زَالَ عَن مَكَانَهُ فصدقوا وَإِذَا سَمِعْتُمْ بِرَجُلٍ تَغَيَّرَ عَنْ خُلُقِهِ فَلَا تصدقوا بِهِ وَإنَّهُ يَصِيرُ إِلَى مَا جُبِلَ عَلَيْهِ ". رَوَاهُ أَحْمَدُ
sunnah.com