Musnad Ahmad 30:723

Sufyan ibn 'Uyaynah narrated to us, from Suhayl, from Abu Salih, from Abu Hurayrah: "A man removed a thorny branch from the path of the Muslims, so he was forgiven." 'Abdullah said: "This hadith is *marfu'* (attributed to the Prophet), but Sufyan fell short in attributing it (fully)."