Ibn Abbas (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "When a man says to another, 'O effeminate one (mukhannath)!', give him twenty lashes; and when he calls someone a Jew, give him twenty lashes as well."
Ibrahim al-Ashhali is alone in narrating it, and he is not strong; if it is authentic, it is to be understood as discretionary punishment (ta'zir).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 17148