Did Abu Bakr Al-Siddiq say, concerning the Christians, "Are you pleased with the triumph of your brethren over our brethren?" And is this permissible?

It is narrated in an athar (narration) reported by Ibn Jarir al-Tabari from Ikrimah that Abu Bakr al-Siddiq, may Allah be pleased with him, said to the disbelievers when they rejoiced at the Persian victory over the Romans: "Are you pleased with the triumph of your brothers over our brothers! Do not rejoice, and may Allah not gladden your eyes, for by Allah, the Romans will surely triumph over Persia." This athar is mursal (a type of weak narration).

Assuming the authenticity of the athar, Abu Bakr's words were a response to the polytheists' statement: "You are People of the Book, and the Christians are People of the Book, and we are unlettered, and our brothers from the people of Persia have triumphed over your brothers from the People of the Book." His response, may Allah be pleased with him, was in keeping with their speech and terminology, which is an aspect of the rhetorical style known as al-mujaraah (concordance), meaning to go along with the interlocutor according to the apparent meaning of their words.

In their statement, there is an indication of the intended meaning of "brotherhood" here, which is their shared characteristic with the Persians of not being People of a Heavenly Book, and the Muslims' shared characteristic with the Christians of being People of the Book. Thus, the Romans are closer to the Muslims than the Persians, and the Persians are closer to the polytheists than the Romans.

In any case, describing disbelievers as brothers is permissible if it refers to lineage, tribe, humanity, and the like. It is not permissible if it refers to religion, affection, or love. The default rule regarding the unqualified use of the term "brotherhood" is prohibition, as Allah Almighty said: "Indeed, the believers are brothers" (Al-Hujurat: 10). This indicates exclusivity, meaning that brotherhood is only among believers.