Riyaa (Showing Off)
The word riyaa is taken from the word ruyah (to be seen). Riyaa is of many types and forms, its nature and tendency is that it invalidates the actions.
The Prophet, peace be upon him, said: "What I fear for you the most is the minor shirk, that is ar-riyaa. Allah will say on the Day of Judgment when He is rewarding the people for their actions: Go to those for whom you did riyaa for in the world then see if you find the reward with them." [Related by Ahmad]
The Prophet, peace be upon him, said: "Shall I not inform you of what I fear for you more than the maseeh ud-dajjaal? It is the hidden shirk. It is when a man stands up for prayer, then beautifies his prayer for another to look at." [Related by Ibn Maajah (2604)]
The scholars and the active worshippers, who made great efforts to tread the path to the Hereafter, were even put to trial by it. When they took control of themselves and abstained from desires, they were not being allured to the apparent and open sins committed by the limbs. However when they became relaxed, they began to pretend to show knowledge, actions and attend gatherings, to be observed by the people with reverence and esteem. They felt great delight and they looked down upon the idea of leaving sins. So while they are thinking that they are from amongst the sincere worshippers of Allah their names have been confirmed as one of the hypocrites. This is a great deception and no one is safe from it except the angels.
O Allah, Lord of the Heavens and the earth, purify our hearts from hypocrisy and our actions from riyaa. Make us firm upon Your straight path so that we achieve certainty. Ameen
Source:
"Invalidation of Actions" - Saleem al-Hilaalee