Enthusiasm when one first repents, followed by slackening off
Question

 
When a person repents, he makes a vigorous start and says, “The Shaytaan is telling me to slow down,” so he does more acts of worship. Then his enthusiasm cools down, and he says, “Allah does not burden any person beyond his scope,” and his acts of worship become less until he goes back to the way he was.
 My question: What advice can you give? Should he make a vigorous start, or take a gradual approach until it is established and then add more after a while, or should he follow the saying, “When your wind blows, then make the most of it”?.
Praise be to Allah.The blessing of guidance and repentance is one of the greatest blessings that Allah can bestow upon the Muslim, whereby he changes himself for the better in ways that will bring him closer to Allah, may He be exalted. Usually the person who has repented starts to do acts of worship in an enthusiastic manner, seeking thereby to make up for what he missed out on during the time that he spent in sin and misguidance. 
This is something natural that happens to everyone who is sincere in his repentance. This was mentioned by our Prophet (peace and blessings of Allah be upon him), who also described the cooling off and reduction of enthusiasm that comes after that. This is also something natural, but the danger in the case of one who has repented is that this loss of enthusiasm may lead to him going back to the way he was. Hence it is essential to pay attention to this matter. If the one who repents finds his enthusiasm waning, he must adopt a moderate approach and adhere to the Sunnah so that he can preserve his capital, then he can start again with energy and strength, because starting from the middle is better than starting from zero. 
It was narrated that ‘Abd-Allah ibn ‘Amr (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “Every deed has a period of enthusiasm, and every period of enthusiasm is followed by a slackening off. If a person’s enthusiasm is for my Sunnah, then he has succeeded, but whoever chooses something else when he slackens off is doomed.”
Narrated by Ibn Hibbaan in his Saheeh (1/187); classed as saheeh by al-Albani in Saheeh al-Targheeb, 56. 
It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: “Every deed has a period of enthusiasm, and every period of enthusiasm is followed by a slackening off. If a person is moderate and avoids extremes, then you may have hope for him, but if fingers are pointed at him, then do not count him as anything.”
Narrated by al-Tirmidhi, 2453; classed as hasan by al-Albani in Saheeh al-Targheeb, 57. 
Al-Mubaarakfoori (may Allah have mercy on him) said: 
“Every deed has a period of enthusiasm” means, enthusiasm and energy for doing a thing, whether it is for good or evil. 
“and every period of enthusiasm is followed by a slackening off” means, one becomes tired, weak and lethargic 
“If a person is moderate and avoids extremes” means, if he controls his enthusiasm and avoids the extremes of excess and negligence when his enthusiasm wanes. 
“then you may have hope for him” means, there is the hope that he will succeed, for he can continue to adhere to something moderate, and the most beloved of deeds to Allah are those which are done consistently. 
“but if fingers are pointed at him” means, he is striving hard in order to become famous for his worship and asceticism, so that he will be famous and people will point at him. 
“then do not count him as anything” means, do not think of him as special or regard him as one of the righteous, for he is showing off. He did not say, “Do not have any hope for him,” because he has already fallen and he cannot catch up with what he has missed. 
Tuhfat al-Ahwadhi, 7/126 
In order for the Muslim to avoid either extreme, he must be moderate and not go to extremes in doing acts of worship and obedience lest he get bored and give it up, and he should not refrain from doing them out of laziness and carelessness lest he gets used to that and never goes back to worship. Both attitudes are wrong, but the one who follows a middle path is following the right path, and whoever follows the right path will attain that which Allah loves and is pleased with. 
It was narrated that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “No one of you will be saved by his deeds.” They said: Not even you, O Messenger of Allah? He said: “Not even me, unless Allah bestows mercy upon me. So do good deeds properly, sincerely and moderately, and worship Allah in the forenoon and in the afternoon and during a part of the night, and always adopt a moderate course whereby you will reach your target (Paradise).”
Narrated by al-Bukhari, 6098 
Al-Haafiz ibn Hajar (may Allah have mercy on him) said:  
“So do good deeds” means, strive to do what is right. 
“moderately” means, do not go to extremes in worship, lest you become tired and give up, and thus fall short. 
This hadeeth indicates that we are encouraged to be gentle and moderate in worship; the words used liken worship to walking at various times of day and night, with the aim of reaching one's abode, namely Paradise. 
“Always adopt a moderate course” means adhere to the middle way. The literal translation would be, “Moderation, moderation”; the word is repeated for emphasis. 
Fath al-Bari, 11/297 
Conclusion: We invite you to ponder the ahaadeeth quoted above and think about what they mean. Remember that the one who repents should be grateful, and the best way of showing gratitude is to persist in repentance, which means persisting in worship. Remember that “The dearest of actions to Allah is that which is done regularly, even if it is small.” Narrated by al-Bukhari and Muslim. So do not start in an overenthusiastic way and then stop completely; rather be moderate in worship. This is something that it is possible for you to do. Whenever you feel more energetic, then focus on obeying and worshipping Allah, and whenever you feel tired than go back to the moderate way. We ask Allah to make things easy for you, and to guide you to the best of words, deeds and attitudes. 
And Allah knows best.