What to say when something that pleases you happens

 242. Whenever something happened that pleased him or made him happy , the Prophet (Peace and Blessings of Allah be upon him) used to prostrate himself in thanks to Allah, the Blessed, the All-Mighty.

Reference: Abu Dawud, Ibn Majah, At-Tirmithi. See also Al-Albani, Sahih Ibn Majah 1/233, and 'Irwa'ul-Ghalil 2/226