Majma al-Zawaid — Hadith 9600

Wabr bin Mushhir narrates: Musaylimah sent me, Ibn Shalghaf and Ibn al-Nawwahah to the Prophet (peace and blessings be upon him). We came to him. My two companions spoke before me, because both of them were older than me. They recited the testimony of faith and then said: "We bear witness that you are a Prophet, and that after you Musaylimah (will be a prophet)." The Prophet (peace and blessings be upon him) asked (me): "O boy! What do you say?" I said: "I bear witness to what you bear witness to, and I declare false what you declare false." The Prophet (peace and blessings be upon him) said: "I bear witness, as many times as the grains of soil of al-Dahna', that Musaylimah is a liar." Then he said: "Seize the two of them." They were seized, and it was ordered that they be kept in the house of Kaysan. One of his Companions interceded for them, so the Prophet (peace and blessings be upon him) let them both go.
Tabarani recorded it. Its chain contains a group of narrators whom I do not know.