Mujahid (may Allah have mercy on him) said that the Prophet (peace and blessings be upon him) sent Abdullah bin Mas'ud and Khabbab (may Allah be pleased with them both) as one detachment, and sent Dihyah (may Allah be pleased with him) alone as a detachment.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18199