What is the ruling on one who swore an oath by divorce upon his wife not to approach her for a month, then had intercourse with her before the month ended? And does divorce occur by his statement: "Upon me be divorce, I will not approach you nor will you approach me for a month"?

The majority of scholars hold that a conditional divorce takes effect when the condition is met. So, if you had intercourse with your wife before the end of the month during which you swore by divorce not to have intercourse with her, then according to the majority of scholars, the divorce has occurred. You may take her back before her waiting period (iddah) ends, provided this divorce does not complete the three divorces. As for the view of Ibn Taymiyyah, you are liable for an expiation for an oath (kaffarat yameen) if you did not intend divorce. The preponderant view is that of the majority of scholars.