Musnad Abu Ya'la al-Mawsili 155:174

Narrated to us Abdullah ibn al-Rumi, narrated to us Abd al-Razzaq, informed us Ma'mar, from al-Zuhri, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (peace be upon him) said: "Good is tied to the forelocks of horses until the Day of Resurrection. And the likeness of the one who spends on them is like the one who stretches out his hand with charity."