A man came to Messenger of Allah ﷺ asking him about Islam, Messenger of Allah ﷺ said, "You have to offer five compulsory prayers in a day and a night (24 hours)." The man asked, "Is there any more compulsory prayers for me?" Messenger of Allah ﷺ said, "No, unless you like to offer Nawafil (i.e. optional prayers)." Messenger of Allah ﷺ then added, "You have to observe fasts during the month of Ramadan." The man said, "Am I to fast any other days?' Messenger of Allah ﷺ said, "No, unless you wish to observe the optional fast voluntarily." Then Messenger of Allah ﷺ told him about the compulsory Zakat. The man asked, "Do I have to give anything besides?" Messenger of Allah ﷺ 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." Messenger of Allah ﷺ said, "If he has said the truth he will be successful."  

أَنَّهُ سَمِعَ طَلْحَةَ بْنَ عُبَيْدِ اللَّهِ يَقُولُ جَاءَ رَجُلٌ إِلَى رَسُولِ اللَّهِ ﷺ فَإِذَا هُوَ يَسْأَلُهُ عَنِ الإِسْلاَمِ فَقَالَ رَسُولُ اللَّهِ ﷺ خَمْسُ صَلَوَاتٍ فِي الْيَوْمِ وَاللَّيْلَةِ فَقَالَ هَلْ عَلَىَّ غَيْرُهَا قَالَ لاَ إِلاَّ أَنْ تَطَّوَّعَ فَقَالَ رَسُولُ اللَّهِ ﷺ وَصِيَامُ رَمَضَانَ قَالَ هَلْ عَلَىَّ غَيْرُهُ قَالَ لاَ إِلاَّ أَنْ تَطَّوَّعَ قَالَ وَذَكَرَ لَهُ رَسُولُ اللَّهِ ﷺ الزَّكَاةَ قَالَ هَلْ عَلَىَّ غَيْرُهَا قَالَ لاَ إِلاَّ أَنْ تَطَّوَّعَ فَأَدْبَرَ الرَّجُلُ وَهْوَ يَقُولُ وَاللَّهِ لاَ أَزِيدُ عَلَى هَذَا وَلاَ أَنْقُصُ قَالَ رَسُولُ اللَّهِ ﷺ أَفْلَحَ إِنْ صَدَقَ  

The Prophet ﷺ said, "Whoever has to take an oath should swear by Allah or remain silent." (i.e. He should not swear by other than Allah.)  

أَنَّ النَّبِيَّ ﷺ قَالَ مَنْ كَانَ حَالِفًا فَلْيَحْلِفْ بِاللَّهِ أَوْ لِيَصْمُتْ