Dawud bin Kurdus states that Sayyiduna Umar (may Allah be pleased with him) made peace with Banu Taghlib on the condition that the sadaqah on them would be doubled, that they would not prevent anyone from accepting Islam, and that they would not dye their children by dipping them in water.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18794