Musnad Abu Ya'la al-Mawsili 155:159

And from al-Awza'i, from Yahya ibn Abi Kathir, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Do not precede Ramadan by a day or two, except for a man who used to fast a fast, so let him fast it."