And it was said to Sahl [rahimahullah] What thing is the most severest upon the Nafs? So he said Al ikhlaas and that is because in it, there isnt in it a share [for other than Allah] Al-Muhadhdhab Min Madaarij As-Saalikeen pg.196


Some of the Salaf said, "Al Ikhlaas is that you do not request by your action a witness other than Allah nor seek to be rewarded from other than Him."


It has been said, Ikhlaas is tasfiyyatul fi'l [purifying the actioon] from the observations of the creation."


Others said, " it is singling out the right of Subhaanahu with respect to [one's] intent in obedience [to Allah]."

Likewise it has been said, "Al Ikhlaas is the loftiest of actions of the slave[of Allah] [both] outwardly and inwardly, and Riyaa [showing off] [happens when] the outward [action] is better than it's inward [action] and being truthful [with respect] to Ikhlaas is that the inward [aspect of it] is more rewarding and prosperous than the outward [expression of it]. pg.195 Al Muhadhdhab....