Mukhtasar Bukhari (Abridged) 618 — Two rak‘ahs before Zuhr are Sunnah

Umm al-Mu'mineen Aisha Siddiqa (may Allah be pleased with her) says that the Prophet Muhammad (peace and blessings be upon him) never used to leave four rak'ahs before Dhuhr and two rak'ahs before Fajr.