This dua has the reward of freeing ten slaves, gaining 100 good deeds, removing 100 bad deeds, protection from Shaythan for the whole day and nobody will be able to do a better deed.

Dua:

Say ‘La ilaha illal-lah wahdahu la sharika lahu, lahu-l-mulk wa lahu-l-hamd wa huwa ‘ala kulli shai’in qadir’ 100 times a day In Shaa Allah.

Translation: ‘None has the right to be worshipped by Allah (SWT) alone, Who has no partner. His is the dominion and His is the praise, and He is Able to do all things’

Hadith:

Narrated by Abu Hurairah: Allah’s Apostle (SAW) said: ”Whoever says: ‘La ilaha illal-lah wahdahu la sharika lahu, lahu-l-mulk wa lahu-l-hamd wa huwa ‘ala kulli shai’in qadir,’ one hundred times will get the same reward as given for manumitting ten slaves; and one hundred good deeds will be written in his accounts, and one hundred sins will be deducted from his accounts, and it (his saying) will be a shield for him from Satan on that day till night, and nobody will be able to do a better deed except the one who does more than he.” – Bukhari, Volume 8, Book 75, Number 412