Yazid bin Hassan (may Allah have mercy on him) narrates from his father that Sayyiduna Abu Hashim bin Utbah bin Rabi'ah (may Allah be pleased with him) had a moustache which he would tie behind the nape of his neck. So I said: What is the matter with your moustache, when what has come from the Prophet (peace and blessings be upon him) about trimming the moustache has come? He said: I had trimmed my moustache, then I came to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) passed his hand over me and said: "When did you trim your moustache?" I said: Just now. He (peace and blessings be upon him) said: "Then do not trim it until you meet me (again)." Then the Messenger of Allah (peace and blessings be upon him) passed away before I met him (peace and blessings be upon him) again, so I will never cut it until I meet him (peace and blessings be upon him).
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7171