It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Twelve thousand men will set out from Aden to help Allah and His Messenger; these people will be the best among all people between me and them."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 3079
Hadith Gradingحکم دارالسلام:إسناده صحيح، قاله أحمد شاكر