It is narrated from Sayyiduna Umayyah bin Amr al-Damri (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) sent him to spy on Quraysh. He said: "I came to the wooden post (on which) Khubayb (was crucified), and I was afraid of the watchmen. I climbed up it and untied him, and he fell to the ground. I withdrew a short distance and sat, then I turned around and could not see the post of Khubayb; it was as if the earth had swallowed him. No trace of Khubayb has been known to this day."
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 852