Musnad Ahmad 30:992

Yahya ibn Adam narrated to us, Ibn al-Mubarak narrated to us, from Ma'mar, from Hammam ibn Munabbih, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "The good word is a charity, and every step you take toward the prayer—or he said: toward the mosque—is a charity."