Is it permissible for us to visit graves while fasting?

There is no impediment to visiting graves while fasting, due to the general nature of the Prophet's (peace and blessings be upon him) statement: "Indeed, visit them." And nothing has come to specify that to a particular time over another. The hadith of Abu Hurairah indicates the virtuous deeds performed by Abu Bakr Al-Siddiq (may Allah be pleased with him) on a single day while he was fasting, and his entry into Paradise thereby.