Musnad Ahmad 30:2123

Khalaf ibn al-Walid narrated to us, he said: Ibn 'Ayyash—meaning Isma'il—narrated to us, from Suhayl, from his father, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "A servant entered Paradise because of a thorny branch that was on the path of the Muslims, so he removed it from them."