(a) Sayyiduna Ibn Umar (may Allah be pleased with them both) said: When these two cities were conquered, they came to Sayyiduna Umar (may Allah be pleased with him) and said: The Messenger of Allah (peace and blessings be upon him) appointed Qarn for the people of Najd, and it lies away from our route; if we go there, it is hard for us. He said: "Look for a point level with it on your route." So he appointed Dhat Irq for them.
(b) Tawus, Jabir bin Zayd Abu al-Sha'tha' and Muhammad bin Sirin held that the Messenger of Allah (peace and blessings be upon him) did not appoint this miqat. This is the position of Imam al-Shafi'i (may Allah have mercy on him). Ata bin Abi Rabah (may Allah have mercy on him) says that the Prophet (peace and blessings be upon him) appointed it, but this is not supported by a chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8913