Mu'adha said she asked ‘A’isha how many <i>rak'as</i> God’s Messenger prayed at the forenoon prayer, and she replied, “Four <i>rak'as</i>, but sometimes more, as God pleased.” Muslim transmitted it.

وَعَن معَاذَة قَالَتْ: سَأَلْتُ عَائِشَةَ: كَمْ كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُصَلِّي صَلَاةَ الضُّحَى؟ قَالَتْ: أَرْبَعَ رَكَعَاتٍ وَيَزِيدُ مَا شَاءَ اللَّهُ. رَوَاهُ مُسلم