Messenger of Allah (ﷺ) said:

Five prayers during the day and the night. (Upon this he said: Am I obliged to say any other (prayer) besides these? He (the Holy Prophet, ) said: No, but whatever you observe voluntarily, out of your own free will, and the fasts of Ramadan. The inquirer said: Am I obliged to do anything else besides this? He (the Holy Prophet) said: No, but whatever you do out of your own free will. And the Messenger of Allah told him about the Zakat (poor-rate). The inquirer said: Am I obliged to pay anything else besides this? He (the Holy Prophet) said: No, but whatever you pay voluntarily out of your own free will. The man turned back and was saying: I would neither make any addition to this, nor will decrease anything out of it. The Prophet remarked: He is successful, if he is true to what he affirms.