Acts 18:20

When they desired him to tarry longer time with them, he consented not;

The verse describes Paul's brief first visit to Ephesus after leaving Corinth while on his way to Jerusalem. He had reasoned with the Jews in the synagogue and made so favorable an impression that they entreated him to continue his labors among them. The Jews at Ephesus desired him to remain longer time with them and continue teaching them. He declined and did not consent to tarry longer because his plan to visit Jerusalem and his journey there prevented him from remaining.

The Jerusalem journey was to attend and celebrate an approaching festival. That festival was Pentecost. He promised to return and labor among them later if God willed. He left Aquila and Priscilla, who had accompanied him to Ephesus, to carry forward the good work he had begun.