I say, and with God's success: It is to say after exiting the restroom: "Your forgiveness"; as narrated by Aisha, may Allah be pleased with her, who said: "The Prophet (peace be upon him) would say when he exited the restroom: 'Your forgiveness.'" This is found in Sunan al-Tirmidhi 1/12, and the wording is his. Al-Tirmidhi said: "This is a good strange hadith; we do not know it except from the narration of Israel from Yusuf ibn Abi Burdah." It is also in Sunan Abu Dawood, 1/55, and Sunan Ibn Majah, 1/110, and in Al-Mustadrak, 1/261, where it is authenticated. Al-Dhahabi said in his summary: "Authentic, and Yusuf is trustworthy." In Sahih Ibn Hibban 4/290, Sheikh Shu'ayb said: "Its chain is good." It seems that the Prophet (peace be upon him) saw that neglecting to mention Allah during the time spent in the restroom was a shortcoming on his part, so he made up for it by seeking forgiveness, for he (peace be upon him) would remember Allah in all his conditions. The seeking of forgiveness here is a metaphor for acknowledging the inadequacy in fulfilling the right of gratitude for the blessing of nourishment and the upbringing of food from the time of consumption until the time of digestion, and facilitating the exit of waste while keeping the body safe from pain. Therefore, he resorted to seeking forgiveness; acknowledging the shortcoming in thanking the blessing. See: Bada'i al-Sanai, 5/126, and Tabyin al-Haqaiq, 1/166, and Fath al-Qadeer, 1/419, and Allah knows best.