It was narrated that Anas bin Malik said:
"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).'"
English reference: Vol. 1, Book 1, Hadith 301
Arabic reference: Book 1, Hadith 320