Al-Hasan (may Allah have mercy on him) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever is summoned to one of the judges and does not respond, he is a wrongdoer."
This is mursal (the Successor narrates it directly from the Prophet).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20485