‘Alee radi Allaahu ‘anhu said:
Knowledge calls out for action, so either it is responded to or else it departs.
And Sufyaan ath Thawree rahimahullaah said:
Knowledge is only to be learned in order for Allaah to be feared and obeyed by it.
And Fudayl ibn ‘Iyaad rahimahullaah said:
The person of knowledge does not stop being jaahil (ignorant) of what he knows until he acts on it. So when he acts on it, he is an ‘aalim (person of knowledge).
And ibn al Jawzee rahimahullaah said:
The true miskeen (impoverished person) is the one whose lifetime is lost in knowledge that he does not act upon. So he has missed out on the delights of the dunyaa and the treasures of the Hereafter.
Thus he will come (on the Last Day) as a bankrupt person, along with having a strong proof against himself.
Quoted in ‘Awaa-iq ut talab of ‘Abdus Salaam ibn Burjiss rahimahullaah pages 17 to 19, translated by Nasser ibn Najam