With regards to the student of knowledge being the foremost to put his knowledge into practice, the scholar Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah stated:
Upon you – baarak Allaahu feekum – is to act upon what you know because this is the fruit of knowledge.
No, what is the benefit of knowledge which the person does not act upon? There is no benefit in it – rather it will be something harmful for the person.
By Allaah, the ignorant person is better than the person of knowledge who does not act upon his knowledge.
So the proof has been established against the person of knowledge who does not act (upon his knowledge) and the excuse has been cut off for him.
So sometimes the ignorant person learns (something) and (then) acts; but as for the man who is a person of knowledge but he does not act, then his knowledge is a harm for him. Therefore the Prophet sall Allaahu ‘alaihi wa ‘alaa aalihi wa sallam said:
The Qur-aan is a proof for you or against you.
And the Qur-aan is knowledge. So as for the person who memorises the Qur-aan, then is the Qur-aan a proof for him?
The Prophet sall Allaahu ‘alaihi wa sallam divided that into two categories. He said:
… a proof for you or against you.
So it is a proof for you if you act upon it and it is a proof against you if you do not act upon it.
Therefore I urge you to act upon what you have learned such that your knowledge becomes a proof for you, and a means to your attaining the everlasting abode of bliss. I ask Allaah that He makes me and you to be from its people.
Therefore it is a must to act (upon knowledge). And let us strike an example for this.
When a person knows that the prayer is obligatory upon him and that it is obligatory for him to establish them with the congregation in the mosques, then is it befitting for him that he neglects this obligation and that he does not pray except when it is easy for him? When he wakes up from his sleep, (only then) does he pray? When he has a break from work (only then) does he pray?
Is this befitting for him whilst he knows that the prayer in congregation is obligatory for him to be negligent about this?
No, this is absolutely unbefitting for him – and if not, then the ignorant person is better than him.
(Quoted in Wasaayaa wa tawjeehaat li tullaab il ilm p178 to 179, translated by Nasser ibn Najam)
Reported by Muslim (223) from the hadeeth of Aboo Maalik al Ash’aree