Fasting continuously means that a person fasts for two or more days without breaking the fast. That is, the fast continues all night and the person does not eat or drink. The Prophet (peace and blessings be upon him) used to fast continuously, and Allah gave him the strength to do that, but he forbade his Ummah to do that out of compassion and mercy towards them.
Dr. Muhammad Ahmad Al-Musayyar, professor of Islamic creed and philosophy at Al-Azhar University, states the following: Almighty Allah ordains that fasting be from dawn to sunset, following which one is permitted to break one’s fast. According to the guidance of Allah’s Messenger (peace and blessing be upon him), it is recommendable that one breaks one’s fast as soon as possible after sunset and has sahur late as possible at night, so that one could be bodily strong and energetic while fasting and working to earn one’s livelihood. That is why the Shari`ah forbids al-wisal fasting, which means to fast for two or more days consecutively without eating or drinking something in between.
However, Allah’s Messenger (peace and blessings be upon him) sometimes performed al-wisal fasting and some of his Companions (may Allah be pleased with them) followed him in this respect. But he (peace and blessings be upon him) forbade them to follow him with regard to al-wisal, as it is difficult on people. This shows how Allah’s Messenger (peace and blessings be upon him) was lenient and merciful towards his nation.
Ibn `Umar (may Allah be pleased with him) was reported in an authentic hadith to have said that the Prophet (peace and blessings be upon him) forbade (his Companions) to observe fast uninterruptedly. But they said, “Messenger of Allah, you yourself observe uninterrupted fast.” He (peace and blessings be upon him) said, “I am not like you. I am fed and provided with water.” And in another wording of the same hadith he (peace and blessings be upon him) was reported to have said, “Who among you is like me? I spend night (in a state) that my Lord feeds me and provides me with water.” The Prophet meant by this that Almighty Allah gave him strength as that of the person who was fed and provided with drink. Hence his words here should not be interpreted literally; otherwise, there would have been no point in his being described as observing uninterrupted fast.
However, the Companions of the Prophet did not refrain from observing that kind of fast with him. Hence, he (peace and blessings be upon him) wanted to teach them an empirical lesson in that respect. According to an authentic hadith, he (peace and blessings be upon him) also observed this fast with them for a day, and then for (another) day. They then saw the new moon and he (peace and blessings be upon him) said, “If the appearance of the new moon had been delayed, I would have observed more (uninterrupted fasts) with you.” According to the narrator of the hadith, he (peace and blessings be upon him) did it as a means of warning them as they had not agreed to refrain.
The Prophet (peace and blessings be upon him) wanted here to prove to his Companions empirically the harmful effect that would have resulted from the uninterrupted fast — their getting bored of worship and falling short of some religious ordinances and social duties.
Based on this, worship should be observed within one’s ability and without excessive exhaustion of oneself lest this may lead to boredom.
Al-Bukhari and Muslim reported on the authority of Masruq that Mother of the Believers `A’ishah (may Allah be pleased with her) was asked “What was the deed most beloved to the Prophet (peace and blessings be upon him)?” She answered, “(It is) that which is constant.”
It was also reported that the Prophet (peace and blessings be upon him) entered onto `A’ishah while a woman was visiting her. He (peace and blessings be upon him) asked, “Who is this (woman)?” `A’ishah said, ”She is so-and-so and she says she offers too much of supererogatory prayers.” He (peace and blessings be upon him) said, “Stop this! Do what you can bear. By Allah! Allah does not cease to reward you unless you get bored (of excessive worship).”
The Prophet’s saying “Stop this” implies reproaching one for overburdening oneself with excessive additional acts of worship and doing what is beyond one’s ability. Unlike the case with doing excessive additional acts of worship, when one commits oneself to doing little acts, one can do them constantly and get their blessings too. The blessings of the regular little acts of worship may even much augment the excessive yet boring ones.