Rashi on Exodus 13:4/רש"י על שמות י״ג:ד׳

1בחדש האביב IN THE MONTH ABIB — But would we not know in which month they went out (even though it were not stated here)? But Moses spake to them as follows: See the kindness which God has bestowed on you — that He brought you forth in a month that is fitted for going out, not hot, nor cold nor rainy. In the same sense it says (Psalms 68:7) “He bringeth forth the prisoners בכשרות” i. e. in a month that is fitted (כשר) for going out (Mekhilta).