Sayyidah Aishah (may Allah be pleased with her) said that when the Messenger of Allah (peace and blessings be upon him) came out of the toilet, he would say: 'Ghufranaka' (O Allah, forgive me).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 461
Yahya bin Abi Bukayr (may Allah have mercy on him) narrates it with the same chain and adds: "(We seek) Your forgiveness, our Lord, and to You is the final return" [Surah al-Baqarah: 285]. [Batil (false)]
(b) Imam Ibn Khuzaymah (may Allah have mercy on him) said that it is reported from Isra'il (may Allah have mercy on him) with the same chain. The Shaykh (may Allah have mercy on him) said: I found this addition only in the narration of Imam Ibn Khuzaymah (may Allah have mercy on him). Then I looked at an old copy of the book of Ibn Khuzaymah (may Allah have mercy on him), and this addition was not in it; it had then been added in its margin in a different handwriting. Most likely it was inserted into his book without his knowledge. 'Wallahu a'lam' (And Allah knows best).
(c) Imam Abu Uthman al-Sabuni (may Allah have mercy on him) narrated it through Abu Tahir, the grandson of Ibn Khuzaymah, from his grandfather without this addition, and by that the falsity of this addition in the hadith is established.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 465