ENOfficial
'A'isha said, "The Prophet, may Allah bless him and grant him peace, was asked, 'Which type of worship is best?' He replied, 'A man's supplication for himself.'"
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عُبَيْدُ اللهِ، عَنِ مُبَارَكِ بْنِ حَسَّانَ، عَنْ عَطَاءٍ، عَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ: سُئِلَ النَّبِيُّ صلى الله عليه وسلم: أَيُّ الْعِبَادَةِ أَفْضَلُ؟ قَالَ: دُعَاءُ الْمَرْءِ لِنَفْسِهِ.
sunnah.com