It is a mitzva for a man to have sexual relations with his wife on the night she immerses in the mikveh (SA EH 76:4). If he does not do so, he has neglected a mitzva of the Torah and violated the severe transgression of causing his wife pain, for it is extremely insulting for a woman to immerse and purify herself only for her husband to have no desire to be intimate with her. This night is considered a set time of ona; if their mitzva is twice a week, then this is considered their first time for that week.
A man about to travel has a mitzva to have sexual relations with his wife the night before his departure (Yevamot 62b; SA EH 76:4), because their yearning to be together is especially strong then, as it is written: “You will know that all is well (shalom) in your tent; when you visit your wife, you will never sin” (Iyov 5:24). In fulfilling this mitzva before traveling, the husband takes leave of his wife with love, joy, and peace (shalom). They will not sin or betray each other while apart, neither in thought nor in deed. However, if the purpose of the journey is to fulfill a mitzva, and if having sexual relations will interfere with that mitzva, then ona is not obligatory (Rashi; Nimukei Yosef).
The mitzva of ona applies before any trip that evokes feelings of separation and longing, which may differ from person to person. Still, minimally, it refers to a trip that involves at least one night away from home. It is also obvious that if the trip will last long enough that they will have to forgo one set ona time, then even without feelings of longing, there is a mitzva for the couple to have sexual relations on the night before departure.
The same law applies when the wife must travel away from home. If her trip prompts feelings of longing or if it causes a set time of ona to be missed, there is a mitzva for her and her husband to have sexual relations the night before she leaves.
When a trip is planned for the day before mikveh night, it is a mitzva to postpone the trip until after the wife immerses and they fulfill the mitzva of ona (Rema, YD 184:10).
Some authorities maintain that there is also a mitzva for a couple to have sexual relations when one of them returns from such a trip (Zohar I 50a; Rashba; Ba’er Heitev 240:19). Certainly, if either spouse wishes to be intimate at this point, all agree that the mitzva of ona applies. It speaks well for their relationship if, after one of them has been away, they wish to be intimate with each other and joyfully fulfill this mitzva.
- Yehoshua b. Levi says, “A man is obligated to have sexual relations with his wife when he departs on a trip, as it says, ‘You will know that all is well in your tent.’” Is the law derived from here? Is it not derived from the verse, “Your desire shall be for your husband,” which teaches that a woman yearns for her husband when he leaves for a trip? R. Yosef answers: “This [extra verse] is not necessary except [to teach us that the obligation applies] near the expected onset of her period.” How close? Rava answers, “A span of twelve hours.” This all applies to [a husband traveling] for something voluntary, but for a mitzva, he is preoccupied.
Many understand the Talmud to mean that since ona is a Torah commandment, even during the time of the month when normally the couple must refrain from sexual relations because she is near the onset of her period, before a trip it is a mitzva for them to have relations, as long as she has not seen blood (Rashi, Raavad, Rashba, Rabbeinu Yeruḥam, Raavan, and SA YD 184:10). Others have a different text of R. Yosef’s statement. Instead of “This [extra verse] is not necessary except [to teach us that the obligation applies] near the expected onset of her period,” the text reads, “This [extra verse] is not necessary except [to teach us that the obligation applies] when his wife is a nidda.” The meaning in that case would be that he should take leave of his wife with words of affection and love (Rabbeinu Tam, R. Zeraḥya Halevi, Rosh, Or Zaru’a, and Smak). Since, according to these poskim, there is no obligation to have sexual relations prior to embarking on a trip, doing so is not permitted near the expected onset of her period. Nevertheless, if she is not expecting her period, and either the husband or wife yearns for intimacy prior to a trip, clearly even these poskim would agree that it is obligatory.