It is reported from Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Pre-emption applies in whatever has not been divided; when boundaries have been established, there is no pre-emption."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشفعة / 11574