Abd al-Malik (may Allah have mercy on him) said: Sayyiduna Umar (may Allah be pleased with him) wrote to Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him): Consult Tulayhah and Amr bin Ma'dikarib (may Allah be pleased with them both) about fighting, but do not entrust any matter to them, for every craftsman knows his own craft best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20329