What is the ruling on praying only fard prayers? I used to always only perform the fard prayers for each prayer. Is all of the prayers I performed invalid?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If you perform the obligatory prayers while observing their due conditions and pillars and avoid the invalidators of the prayer, then they are valid. What is obligatory on a Muslim is to perform the five daily prayers in a day and night, as evidenced by the Hadeeth reported by Al-Bukhaari, Muslim and others on the authority of Talhah ibn ‘Ubaydillaah who said: "'A man from Najd with disheveled hair came to the Messenger of Allah . We heard his loud voice but we did not understand what he was saying, until he came near. He was asking about Islam, so the Messenger of Allah said: 'Five obligatory prayers in a day and night.' The man asked, 'Are there any other prayers due upon me?' The Prophet said: 'No, unless you wish to perform voluntary prayers.' The Messenger of Allah added: 'And fasting the month of Ramadhaan.' The man said, 'Am I required to fast on any other days?' The Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: 'No, unless you wish to observe voluntary fasting.' The Messenger of Allah then told him of the obligatory Zakaah. The man asked, 'Do I have to give anything else besides it?' The Messenger of Allah said: 'No, unless you wish to give in charity voluntarily.' So the man departed, saying, 'By Allah, I will neither do more nor less than that.' The Messenger of Allah said: 'If he is telling the truth, he will be successful.'”

However, the Muslim should not abandon the voluntary prayers, especially the Rawaatib (confirmed voluntary prayers before or/and after obligatory prayers) that the Prophet, sallallaahu ‘alayhi wa sallam, observed regularly and urged us to perform. Voluntary prayers are of major importance because they amend any shortage and deficiency that may occur in the obligatory prayers. It was narrated that the Prophet said: “The first deed a slave of Allah will be held accountable for on the Day of Judgment will be his prayers. If they are good (properly performed), he will have prospered and succeeded, and if they are defective, he will have failed and lost. If there is something missing in his obligatory prayers, The Lord Almighty will Say, ‘See if My slave has (performed) any voluntary prayers with which to complete the deficiency in his obligatory prayers.’ Then, the rest of his deeds will be judged in the same manner.” [Ibn Maajah and At-Tirmithi]

Moreover, performing voluntary acts of worship is a means to earn the love of Allah, The Almighty, and to have one’s supplications accepted. The Hadeeth Qudsi reads: “…and My slave keeps on drawing closer to Me by virtue of performing voluntary acts of worship until I love him. If I love him, I become his hearing with which he hears, his sight with which he sees, his hand with which he strikes, and his leg with which he walks; and if he asks Me (for something), I shall give him, and if he asks for My protection, I shall protect him…”

Allah Knows best.