"I heard my father say: 'I entered upon 'Aishah, and I heard her say: "When the Messenger of Allah exited the toilet, he would say: Ghufranaka (I seek Your forgiveness).'" (Sahih)

Another chain with similar wording.
Sunan Ibn Majah Book 1, Hadith 34
← Previous Hadith The Messenger of Allah said: "None of you should fail to say, when he enters his toilet: 'Allahumma inni a`udhu bika minar-rijsin-najis, al-khabithil-mukhbith, ash-Shaitanir-rajim (O Allah, I seek refuge with You from the filthy and impure, the evil one with evil companions, the accursed Shaitan).'" (Da'if)

Another chain with a slightly different wording from Ibn Abi Maryam who mentioned similar, but he did not say in his narration: "Minar-rijsin-najis (From the filthy and the impure)" he only said: "Minal-khabithil-mukhbith, ash-Shaitanir-rajim (From the evil one with evil companions, the accursed Shaitan)."

Sunan Ibn Majah Book 1, Hadith 33 Next Hadith → "Whenever the Prophet exited the toilet, he would say: 'Al-hamdu lillahilladhi adhhaba 'annial-adha wa 'afani (Praise is to Allah Who has relieved me of impurity and given me good health).'"

Sunan Ibn Majah Book 1, Hadith 35