Sahih Bukhari Volume 2, Book 25, Hadith 1532

حَدَّثَنِي عَلِيُّ بْنُ مُسْلِمٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ لَمَّا فُتِحَ هَذَانِ الْمِصْرَانِ أَتَوْا عُمَرَ فَقَالُوا يَا أَمِيرَ الْمُؤْمِنِينَ، إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم حَدَّ لأَهْلِ نَجْدٍ قَرْنًا، وَهُوَ جَوْرٌ عَنْ طَرِيقِنَا، وَإِنَّا إِنْ أَرَدْنَا قَرْنًا شَقَّ عَلَيْنَا‏.‏ قَالَ فَانْظُرُوا حَذْوَهَا مِنْ طَرِيقِكُمْ‏.‏ فَحَدَّ لَهُمْ ذَاتَ عِرْقٍ‏

Narrated By Ibn Umar : When these two towns (Basra and Kufa) were captured, the people went to 'Umar and said, "O the Chief of the faithful believers! The Prophet fixed Qarn as the Miqat for the people of Najd, it is beyond our way and it is difficult for us to pass through it." He said, "Take as your Miqat a place situated opposite to Qarn on your usual way. So, he fixed Dhatu-Irq (as their Miqat)."