Zayd ibn Aslam reported from his father that 'Umar used to say on the minbar, "O people! Improve your homes but be careful about these house snakes before they make you afraid. Those among them which are Muslim will not be clear to you and, by Allah, we have not made peace with them since the time when we treated them as an enemy."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْدُ اللهِ بْنُ يُوسُفَ، قَالَ: حَدَّثَنَا اللَّيْثُ، قَالَ: حَدَّثَنَا ابْنُ عَجْلاَنَ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ أَبِيهِ قَالَ: كَانَ عُمَرُ يَقُولُ عَلَى الْمِنْبَرِ: يَا أَيُّهَا النَّاسُ، أَصْلِحُوا عَلَيْكُمْ مَثَاوِيكُمْ، وَأَخِيفُوا هَذِهِ الْجِنَّانَ قَبْلَ أَنْ تُخِيفَكُمْ، فَإِنَّهُ لَنْ يَبْدُوَ لَكُمْ مُسْلِمُوهَا، وَإِنَّا وَاللَّهِ مَا سَالَمْنَاهُنَّ مُنْذُ عَادَيْنَاهُنَّ.
sunnah.com