Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.020C.

Section : Entering the bathroom.

One should enter the bathroom or a privy with his left foot, and exit with his right foot, saying: “O Allah! I seek your forgiveness.” ‘Aishah related that when the Messenger of Allah left the bathroom, he would say this supplication. (Related by “the five,” except for an-Nasa’i.) What ‘Aishah stated is the soundest statement on this topic. It is related through a number of weak chains that the Prophet, upon whom be peace, used to say, “Praise be to Allah who made the filth leave me and who has given me health,” and “Praise be to Allah who let me enjoy it, kept for me its energy and relieved me of its harm.”