sreyah-srtim bhaktim udasya te vibho
klisyanti ye kevala-bodha-labdhaye
tesam asau klesala eva sisyate
nanyad yatha sthula-tusavaghatinam
sreyah-srtim—the auspicious path of liberation; bhaktim—devotional service; udasya—giving up; te—of You; vibho—O my Lord; klisyanti—accept increased difficulties; ye—all those persons who; kevala—only; bodha-labdhaye—for obtaining knowledge; tesam—for them; asau—that; klesalah—trouble; eva—only; sisyate—remains; na—not; anyat—anything else; yatha—as much as; sthula—bulky; tusa—husks of rice; avaghatinam—of those beating.
" 'My dear Lord, devotional service unto You is the only auspicious path. If one gives it up simply for speculative knowledge or the understanding that these living beings are spirit soul and the material world is false, he undergoes a great deal of trouble. He only gains troublesome and inauspicious activities. His actions are like beating a husk that is already devoid of rice. One's labor becomes fruitless.'
This is a quotation from Srimad-Bhagavatam (10.14.4).
Link to this page: https://prabhupadabooks.com/cc/madhya/25/31