Allah has prescribed for us the supererogatory acts of worship in order to complete the obligatory acts.
Someone is asking about the ruling on performing the obligatory prayers only, without the supererogatory ones?
Answer:
It is known that supererogatory acts of worship are a blessing of Allah for Muslims, as they are considered a means of complement for the obligatory ones. Moreover, it is a great risk for a Muslim to be content only with performing the obligatory acts of worship as no one would perform them perfectly.
So, a good practicing Muslim is highly recommended to save no efforts to offer as many supererogatory acts of worship as he can to make up for any shortage in or imperfectness in the obligatory ones.
Responding to your question, Sheikh `Abdel Khaliq Hasan Ash-Sharif, a prominent Muslim scholar, Egypt, stated,
Thank you for your question.
Talhah ibn `Ubayd-Allah said: “A man came to the Prophet (peace be upon him) and when he drew close to him he asked him about Islam. The Prophet said:’Five prayers each day and night.’ He said, ‘Do I have to do anything else?” He said, “No, not unless you do it voluntarily.” And the Prophet said: ‘And fasting Ramadan. ‘He said: ‘Do I have to do anything else?” He said: ‘No, not unless you do it voluntarily.’ And the Prophet (peace be upon him) told him about zakah (obligatory alms). He said: ‘Do I have to do anything else?’He said: ‘No, not unless you do it voluntarily.” The man left, saying, ‘By Allah, I will not do any more than this or any less. ‘The Prophet (peace be upon him) said: ‘He will succeed, if he is speaking the truth.” (Al-Bukhari and Muslim)
Thus if you are able to perform only obligatory prayers perfectly, there is no harm but this is actually unattainable. Who among us offers Prayers with utmost submission and reverence? Who among us does not become occupied with worldly matters during Prayers?
Allah has prescribed for us the supererogatory acts of worship in order to complete the obligatory acts that have not been offered perfectly.
It is reported that the first thing a Muslim will be questioned about is the Prayer. Then, if it fails to be perfect, Almighty Allah says, “Look for supererogatory acts of worship by my servant.” Then, his acts will be completed with them.
It is a mercy and favor from Allah that He prescribed the supererogatory acts of worship for us to complete the obligatory acts.