It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him) wiped phlegm or saliva with his blessed hand and cleaned it, then he had saffron brought and applied it over that spot. Sayyiduna Ibn Umar (may Allah be pleased with them both) says, for this reason saffron is applied in mosques.