What is your advice to someone who has stopped praying the Sunnah prayers in the daytime and does not pray anything at night?
Answer: By Shaykh Muhammad 'Umar Baazmool, instructor at Umm Al-Quraa University in Makkah.
"There is nothing more outstanding as advice than the hadeeth of the Messenger (sallallaahu 'alayhi wa sallam), when he said:
"The very first thing a servant will be asked about on the Day of Judgement is the prayer. If it is found to be deficient, then it will be said, 'Doesn't he have any optional prayers?' If it is found that he has optional prayers, then they will fill the void, and thus his prayers will be accepted, and the rest of his deeds will also be accepted." 
And the Messenger (sallallaahu 'alayhi wa sallam) was asked about a dream that Ibn Umar had, so he (sallallaahu 'alayhe wa sallam) said: "What a good man 'Abdullaah ibn Umar is, so long as he prays at night." 
So then consistently praying the optional prayers, the most important of them being the Witr prayer and the (12) Sunnahs throughout the day and night, is from the most important of all affairs to the Muslim. This is because you, O Muslim, by way of them, compensate for the lapses found in your obligatory prayers.
And the Prophet (sallallaahu 'alayhi wa sallam) clarified in a hadeeth that a man may pray but he may only be credited with half of it, another may pray but only be credited with one third of it, and another may pray but only be credited with one fourth of it.  The meaning is that it often occurs that the people have shortcomings in their prayers, while it is obligatory to offer them, completing them perfectly. So have you actually offered all of your prayers completely and perfectly according to the Shari'ah?
So then you must take care to consistently offer optional prayers, you must take care to consistently offer the Witr prayer, you must take care to offer the other optional prayers consistently. It has been related that Imam Ahmad said about the one who does not consistently pray the Witr prayer, "He is an evil man, his witness is not to be accepted."
So how could a Muslim who has no work keeping him from his worship become lazy and then abandon these (optional) prayers. No doubt, he has caused himself to lose a great amount of good, and to miss an opportunity to obtain tremendous virtues, while being free to do them and try to keep consistency in offering them. I ask Allaah to excuse us and him, and to be gracious.
There is a hadeeth of the Messenger (sallallaahu 'alayhi wa sallam): "May Allaah have Mercy on the one who offers four (rak'ahs) before 'Asr prayer." 
When you do not pray this prayer, four rak'ahs before the 'Asr prayer, you have prevented your own self from being included in those whom the Messenger (sallallaahu 'alayhe wa sallam) supplicated for, those who pray this prayer.
The Messenger (sallallaahu 'alayhi wa sallam) said: "Whoever consistanly prays twelve rak'ahs throughout the day and night, a palace will be built for him in Paradise." 
When you abandon the rawaatib prayers, and you do not pray these twelve rak'ahs, you have deprived your own self from this virtue. Most of the optional prayers have great virtues attached to them, described by the Messenger (sallallaahu 'alayhi wa sallam). So then, O Muslim, how can you lose out, how can you not be concerned about it?
And Allaah knows best.
 Collected by At-Tirmithee, Aboo Daawood, An-Nasaa'ee, and others, see Saheeh Al-Jaami'is-Sagheer wa Ziyaadah #2020.
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