Al-Adab Al-Mufrad, Book 53, Hadith 1251 (In-Book) ⓘ

It is reported that al-Hasan said, "Are you not astonished by this man? (i.e. Malik ibn al-Mundhir) He went to some of the old people of Kaskar who had become Muslim and examined them and then commanded that they be circumcised although it was winter. I heard that some of them died. Greeks and Abyssinians became Muslim with the Messenger of Allah, may Allah bless him and grant him peace, and they were not examined at all."

حَدَّثَنَا مُحَمَّدٌ، قَالَ‏:‏ أَخْبَرَنَا عَبْدُ اللهِ، قَالَ‏:‏ أَخْبَرَنَا مُعْتَمِرٌ قَالَ‏:‏ حَدَّثَنِي سَالِمُ بْنُ أَبِي الذَّيَّالِ، وَكَانَ صَاحِبَ حَدِيثٍ، قَالَ‏:‏ سَمِعْتُ الْحَسَنَ يَقُولُ‏:‏ أَمَا تَعْجَبُونَ لِهَذَا‏؟‏ يَعْنِي‏:‏ مَالِكَ بْنَ الْمُنْذِرِ عَمَدَ إِلَى شُيُوخٍ مِنْ أَهْلِ كَسْكَرَ أَسْلَمُوا، فَفَتَّشَهُمْ فَأَمَرَ بِهِمْ فَخُتِنُوا، وَهَذَا الشِّتَاءُ، فَبَلَغَنِي أَنَّ بَعْضَهُمْ مَاتَ، وَلَقَدْ أَسْلَمَ مَعَ رَسُولِ اللهِ صلى الله عليه وسلم الرُّومِيُّ وَالْحَبَشِيُّ فَمَا فُتِّشُوا عَنْ شَيْءٍ‏.‏