Law relating to the Mezuzah

This is referenced in Kitzur Schulchan Aruch Volume I Chapter 11.

Upon leaving the house and putting one's hand on the Mezuzah, one should say Psalm 121 verses 4, 5, 8.

Transliteration:
4. Hinneh Lo Yanoom Welo Yeeshan, Shomer Yisrael.
5. Adho-nai Shomrekha, Adho-nai Sillekha ‘Al Yad Yemeenekha.
8. Adho-nai Yishmor Sethkha Ubo-ekha, Me’attha We’ad ‘Olam.

English Translation:
"Hashem is my keeper, Hashem is the shade upon my right hand; Hashem will guard my departure and my arrival from this time until eternity."