Reference for Pesachim 207:1
והא מר לא תלתא אמר ולא שבע אמר א"ל איברא בין יום השביעי לששת ימי המעשה מעין חתימה היא ואמר רב יהודה אמר שמואל המבדיל צריך שיאמר מעין חתימה סמוך לחתימתו ופומבדיתאי אמרי מעין פתיחתן סמוך לחתימתן
But you said neither three nor seven? '<span class="x" onmousemove="('comment',' But four.');"><sup>1</sup></span> 'It is true,' answered he, '"between the seventh day and the six working days" is of the nature of the conclusion,<span class="x" onmousemove="('comment',' Habdalah ends with, 'Blessed art thou, O Lord, who makest a division between holy and non-holy'. This phrase, 'between the seventh day' etc. is similar in meaning, and forms a natural bridge to the conclusion, as it were; hence it is not counted. - All benedictions commence with the formula, 'Blessed art thou, O Lord, our God, King of the universe'; if lengthy, they conclude with the formula, 'Blessed art thou, O Lord, who 'etc. It is this latter formula which is referred to as the conclusion.');"><sup>2</sup></span>