La ilaha illa Allah, alone, a hundred times
Man qala: La ilaha illa-llah wahdahu la sharika lah, lahu-l-mulku wa lahu-l-hamd, wa huwa ala kulli shay'in qadir, fi yawmin mi'ata marrah, kanat lahu adla ashri riqab, wa kutibat lahu mi'atu hasanah, wa muhiyat anhu mi'atu sayyi'ah.
"Whoever says: La ilaha illa Allah, alone with no partner; to Him belongs the dominion and to Him belongs all praise, and He is over all things capable, one hundred times in a day, it is for him equal to freeing ten slaves, a hundred good deeds are recorded for him, and a hundred sins are wiped from him."
Narrated by Abu Hurayrah. Sahih al-Bukhari 3293, Sahih Muslim 2691
A short reflection
Three returns in one transaction: freedom, addition, subtraction. Plus a shield from Satan until evening. The economics make no sense in the dunya.