Rashi on Genesis 8:8/רש"י על בראשית ח׳:ח׳

1וישלח את היונה AND HE SENT FORTH A DOVE at the end of seven days, for it is written, (Genesis 8:10) “And he stayed yet other seven days” — from this statement you may infer that after the first occasion, also, he waited seven days.

2וישלח And HE SENT FORTH — This does not mean merely “sending on an errand”, but “sending away”, “letting go” — he freed her to go where she liked, and thus he could see whether the waters abated, because if she could find a resting place she would not return to him.