Matthew 21:20 - Ellicott's Commentary On The Whole Bible

And when the disciples saw it. — Here again St. Mark’s narrative (Mark 11:20-21) seems at once the fullest and the most precise. As he relates the facts, the disciples did not perceive that the fig-tree was withered away till they passed by on the following morning. Peter then remembered what had been said the day before, and, as the spokesman of the rest, drew his Master’s attention to the fact. The immediate withering may have been inferred from its completeness when seen, or its beginning may have been noticed by some at the time.