سنن النسائي

It was narrated that Jabir bin Abdullah said: "When the Prophet (ﷺ) started to pray, he would say the takbir, then say: 'Inna salati wa nusuki wa mahyaya wa mamati lillahi rabbil-alamin, la sharika lahu, wa bidhalika umirtu wa ana min al-muslimin. Allahummahdini liahsanil-amali wa ahsanil-akhlaqi la yahdi li ahsaniha illa anta wa qini sayy'al-a'mali wa sayy'al-ahaqi la yaqi sayy'aha illa ant. (Indeed my salah (prayer), my sacrifice, my living, and my dying are for Allah, the Lord of all that exists. He has no partner. And of this I have been commanded, and I am one of the Muslims. O Allah, guide me to the best of deeds and the best of manners, for none can guide to the best of them but You. And protect me from bad deeds and bad manners, for none can protect against them but You.) "