Musannaf Ibn Abi Shaybah 23220 — A Jew, a Christian and a slave giving

Al-Zuhri and Qatadah said: If a person of the Book, a slave and a child are witnesses, and then the person of the Book becomes a Muslim, the slave is freed and the child grows up, it is valid for them to give their testimony. However, if their testimony was rejected while they were in their former state, then it is not permissible.