Zakariyya narrates from al-Sha'bi (may Allah have mercy on him) that death came to a Muslim man at the place called "Daquqa", and there was no Muslim present to witness his will. So he took two People of the Book as witnesses. They came to Kufah, to al-Ash'ari (may Allah be pleased with him), informed him, and brought his estate and his will. Al-Ash'ari (may Allah be pleased with him) said: This is a matter that has not occurred since the one that happened in the time of the Messenger of Allah (peace and blessings be upon him). He made the two of them swear by Allah after the Asr prayer that they had not betrayed, lied, altered, concealed or changed anything, and that this was the man's will and his estate. Thus he enforced their testimony.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20626
Al-Sha'bi (may Allah have mercy on him) narrates from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) permitted the testimony of the Jews against one another.
In the narration of Ibn Abdan: (he permitted) the testimony of the People of the Book against one another.
Abu Khalid al-Ahmar narrated it thus from Mujalid, and it is one of his errors; others narrated it from Mujalid, from al-Sha'bi, from Shurayh as his own statement and ruling, not marfu' (not attributed to the Prophet).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20627
Al-Sha'bi (may Allah have mercy on him) says that Qadi Shurayh (may Allah have mercy on him) used to accept the testimony of the followers of each religion against those of their own religion, but he did not consider the testimony of a Jew against a Christian, or of a Christian against a Jew, permissible. However, he accepted the testimony of Muslims against everyone, because their testimony is valid against all.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20628
Al-Sha'bi (may Allah have mercy on him) narrates from Qadi Shurayh (may Allah have mercy on him) regarding 'or two others from outside you' [Surah al-Ma'idah: 106]: When a Muslim dies in a foreign land and no Muslim is present there, then the testimony of non-Muslims is permissible at that time. (If two Muslims testify against it, their testimony is accepted) and the testimony of the non-Muslims will be rejected.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20629
Ibrahim (may Allah have mercy on him) narrates from Qadi Shurayh (may Allah have mercy on him) that the testimony of a Jew or a Christian against a Muslim is valid only in a bequest, not otherwise, and this too is restricted to travel.
(b) Yahya bin Wathhab (may Allah have mercy on him) says that Qadi Shurayh (may Allah have mercy on him) considered the testimony of the People of the Book against one another permissible.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20630