Al-Kāfi - Volume 7 > Testimony of the Members of all other Nations
Hadith #5

5- مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ أَبِي نَجْرَانَ عَنْ مُحَمَّدِ بْنِ حُمْرَانَ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) قَالَ سَأَلْتُهُ عَنْ نَصْرَانِيٍّ أُشْهِدَ عَلَى شَهَادَةٍ ثُمَّ أَسْلَمَ بَعْدُ أَتَجُوزُ شَهَادَتُهُ قَالَ نَعَمْ هُوَ عَلَى مَوْضِعِ شَهَادَتِهِ.

5. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ibn abu Najran from Muhammad ibn Humran who has narrated the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about a Christian man who bears a testimony, then becomes a Muslim if his testimony is acceptable. He (the Imam) said, ‘Yes, he is in the right position to testify.’”