There are several occasions during the month when relations between husband and wife are forbidden even though the wife is not in a state of Nidda, since the onset of Nidda is anticipated. In order to avoid committing the grave prohibition of Nidda, a husband and wife must abstain during these periods.
In the case of a woman who does not have a fixed cycle, there are three occasions when abstention is required. One such period is called "Ona Benonit," referring to the thirtieth day since the previous sighting of blood. If the previous sighting occurred during the day, then the husband and wife must abstain during the thirtieth day since the last sighting, from sunrise to sunset, and they may resume relations at night, after the woman performs a Bedika and no bleeding is discovered. If the previous sighting occurred at nighttime, then they must abstain during the thirtieth night – from sundown to sunrise – and may resume the next morning once the wife performs a Bedika.
The second occasion is the "Onat Hahaflaga," referring to the completion of the previous interval. Meaning, if a woman experienced the onset of Nidda twenty-eight days after her previous onset of Nidda, then she and her husband must abstain twenty-eight days later. Once again, they abstain either during the day or during the night, depending on when the previous sighting of blood occurred. Thus, for example, if the wife experienced bleeding during the night twenty-eight days after her previous sighting of blood, they must observe a period of abstention on the twenty-eighth night since that sighting. The next morning, assuming she did not experience bleeding, she performs an inspection, and if she does not discover any blood, relations are permissible. On the thirtieth night, however, they must again abstain, in observance of the "Ona Benonit." Once again, she performs an inspection in the morning and then relations may be resumed.
The third period of abstention is the "Onat Ha’hodesh," the day of the month on which bleeding occurred during the previous cycle. A woman who experienced bleeding on Asara Be’Tebet, for example, would observe a period of abstention – either during the day or during the night, depending on when the bleeding had occurred – on the tenth of Shebat, one calendar month later. The "Onat Ha’hodesh" often coincides with the "Ona Benonit," depending on whether the previous month was twenty-nine or thirty days.
Hacham Ovadia Yosef writes that these periods are determined based upon the first flow of blood. Meaning, if a woman experiences bleeding for several days, the days of abstention are determined based on the day when the bleeding began.
If a woman began experiencing bleeding shortly before sunrise, and it continued until after sunrise, then she observes her periods of abstention at nighttime the next month, but must continue into the morning, as well. For example, if sunrise occurred at 6am, and the bleeding began at 5:45am and continued until 6:15, she must observe the three periods mentioned above during the nighttime, but continue for fifteen minutes into the morning. She would then perform the Bedika fifteen minutes after sunrise. This is the ruling of Hacham Ovadia Yosef.
Hacham Ovadia further writes that if a woman regularly experiences the onset of Nidda at around sunrise, but she is unsure whether it occurred before sunrise or after sunrise, she observes her three Ona periods during the day, and not at night.
In light of these Halachot, it is imperative that women keep calendars and mark down when they begin bleeding each month so that they can calculate the three periods of abstention that must be observed. If a woman neglected to record this information, and she cannot remember when the onset of Nidda occurred, she observes only the "Ona Benonit" on the thirtieth day. She does not have to observe multiple Ona periods for the "Haflaga" and "Hodesh" periods. Needless to say, however, she must ensure not to get into such a situation, and to always make a point of marking down the information so that she and her husband know when to observe the Ona periods.
