Musnad Ahmad 30:877

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, I heard al-'Ala' narrating from his father, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, that he said: "Shall I not guide you to that by which Allah raises the ranks and wipes away the sins?" [They said:] "Yes, O Messenger of Allah." He said: "Abundance of steps to the mosques, waiting for the prayer after the prayer, and performing wudu' thoroughly despite difficulties."