Dua for leaving the house:

بِسْمِ اللّٰهِ، تَوَكَّلْتُ عَلَى اللّٰهِ، وَلَا حَوْلَ وَلَا قُوَّةَ إِلَّا بِاللّٰهِ

Transliteration: Bismillaahi, tawakkaltu ‘alallaahi, wa laa hawla wa laa quwwata illaa billaah

Translation: “In the Name of Allah, I have placed my trust in Allah; there is no might and no power except by Allah.”

The source of this Dua is the following Hadith:

Narrated Anas ibn Malik:

The Prophet (ﷺ) said: When a man goes out of his house and says: “In the name of Allah, I trust in Allah; there is no might and no power but in Allah,” the following will be said to him at that time: “You are guided, defended and protected.” The devils will go far from him and another devil will say: How can you deal with a man who has been guided, defended and protected? [Abu Dawud & At-Tirmidhi]

Also see Dua for entering the house