What is the ruling regarding a diabetic patient, and is it permissible for him to attempt fasting?

If fasting is difficult for a sick person and harms them, then it is not permissible for them to fast, due to Allah's saying: "And do not kill yourselves." Sheikh Al-Uthaymeen, may Allah have mercy on him, gave examples of illnesses that prevent fasting, such as diabetes and kidney disease. The questioner is advised to consult a doctor to ascertain the extent of harm fasting would cause in their condition, and then act upon their advice.