Sayyiduna Anas (may Allah be pleased with him) narrates: The caller of the Prophet (peace and blessings be upon him) came (to some people) and said: "The qiblah has been changed." The imam was in the prayer at that time and had already prayed two rak'ahs. The caller said: "The qiblah has been turned towards the Ka'bah, so pray the remaining two rak'ahs facing the Ka'bah."
Al-Bazzar recorded it, and its chain is hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 1971