It is narrated on the authority of Aisha (RA) that the Messenger of Allah (ﷺ) used to say when he came out of the toilet:

غُفْرَانَكَ

Gufraanak

I ask You (Allah) for forgiveness. Ayesha (RA) said that Rasoolullah (ﷺ) used to say this dua when he came out of the toilet.

Reference: Sahih (Albani). Abu Dawud: 30