It is narrated from Sayyiduna Abd al-Rahman bin Awf (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The prayer of al-hajir (midday) is part of the night prayer." The narrator said: I asked Abd al-Rahman bin Humayd about "al-hajir" and he said: When the sun passes the meridian.
Hadith Referenceالمعجم الكبير للطبراني / العشرة / 280