Gemara

(Beraisa): If a man returned home from his work, from visiting mourners or a celebration, his wife is Muchzekes Tehorah. He may be with her, whether she is sleeping or awake;

This is if she was Tehorah when he left.

Question: Shmuel holds that if she is awake, she must check herself, and even if she is asleep, if she does not have a Veses!

Answer: The case is, she has a Veses. Since he is Tove'a (requests Bi'ah), this is the ultimate Bedikah!

15a (Mishnah): If a man returns from traveling, his wife is Muchzekes to be Tehorah.

(Rabah bar bar Chanah): The Mishnah is even if he returned after her Veses came.

He holds that Vestos are mid'Rabanan.

(R. Yochanan): If a woman has a Veses, her husband (when he returns) can calculate when her last sighting should have been. If enough time elapsed since then for her to immerse, he may assume that she is Tehorah.

(R. Aba): He permits when it is possible that she never became Teme'ah, for then, even if she saw, perhaps she immersed;

If she definitely was Teme'ah, and we are in Safek whether or not she immersed, this Safek does not overturn what was certain.

(Rav): If a woman did not check herself at the time of her Veses, and checked herself later and found herself to be Tehorah, she is Tehorah;

(Shmuel): She is Teme'ah. We assume that the blood came in its usual time.

(Rav Nachman bar Yitzchak): They argue about whether Vestos are mid'Oraisa.

(Rav Sheshes): Rav and Shmuel argue as the following Tana'im do:

(Beraisa - R. Eliezer): (If a woman did not check herself at the time of her Veses), she is (Muchzekes to be) a Nidah;

R. Yehoshua says, she checks herself later. (If she finds herself to be Tehorah, she is Tehorah.)

In another Beraisa, R. Meir holds like R. Eliezer, and Chachamim hold like R. Yehoshua.

Rishonim

Rif (Shevu'os 4b): If one returns from a journey, his work, a wedding or mourner's house, he may cohabit with his wife, whether she is awake or asleep, but only if he left her in Chezkas Taharah.

Ran (DH v'Garsinan): R. Yochanan permits if there was enough time after her Veses to become Tehorah, for it is a Sefek-Sefeka. We need not say that he argues with Rabah bar bar Chanah. R. Yochanan discusses one who dwells in the city, so there is no Tevi'ah, so he must calculate. Alternatively, also R. Yochanan discusses one who returned from a journey (and he is concerned for the Onah (30 days, the average period of Stam women) if this is after the Veses, like the Ramban explains). Likewise, sometimes he is lenient to assume that she saw at the time of the Veses, when this would allow her enough time to immerse afterwards, but there would not be time if she saw in the Onah (day 30) afterwards. Rabah bar bar Chanah assumes that she saw in the Onah afterwards to be lenient. We are always lenient to attribute the sighting to the Veses. However, the Ra'avad says that Rabah bar bar Chanah and R. Yochanan argue. Even though Vestos mid'Rabanan, R. Yochanan requires calculating, even for one who comes from the road. A Veses does not remove from Chezkas Tum'ah without checking. The Ra'avad rules like R. Yochanan. He is concerned for a Veses when she has a Veses, and he is concerned for the Onah when she has no Veses. There is no source to be concerned for both of them together. The Rif wrote that the wives of the donkey-drivers and workers are in Chezkas Taharah. He did not distinguish between whether or not the Onah or Veses came. Also the Rambam says that if one returns home, his wife is in Chezkas Taharah. He may have Bi'ah with not at the time of her Veses, without concern lest she is Nidah. This connotes that he is concerned only for the Onah (time) of her Veses, but not afterwards at all. It seems that they explain that 'within the days of her Onah' is the time of the Veses, but not the day (30) of the Onah itself. We do not say that Chachamim were lenient for one who came from a journey, and were not concerned even for the time of the Veses. They hold that R. Yochanan holds that Vestos mid'Oraisa, unlike Rabah bar bar Chanah. We hold like Rabah, for the Sugya holds that Vestos mid'Rabanan.

Ran (ibid.): Below we say that she must check. This is when he dwells in the city, but not if he came from a journey. Since he was Tove'a, this is the ultimate Bedikah. I do not understand how this helps when she is asleep. There is no Tevi'ah! Do not say that there is Tevi'ah even when she is asleep, for if so, in Nidah (12a) we did not need to answer that she has a Veses. Even if she has no Veses, we can say that there was Tevi'ah! Rather, there is no Tevi'ah when she is asleep. I answer that the Rif and Rambam hold that Chachamim (and R. Yehoshua), who say that she must check, come to argue with the first Tana, who says that if she did not check, she is Temei'ah, for Vestos mid'Oraisa. They disagree, and obligate checking at the time of the Veses. I.e. this is the only stringency of Vestos. It is mid'Rabanan. This is a good answer for the Rif and Rambam, but it is an excessive leniency not to be concerned for the Veses or Onah at all, even for many days, and even if she is sleeping.

Rambam (Hilchos Isurei Bi'ah 4:9): Any woman with a Veses is in Chezkas Taharah to her husband until she tells him 'I am Temei'ah', or until she is established to be Nidah among her neighbors. If he went abroad and left her Tehorah, when he returns, he need not ask her. Even if he found her sleeping, he may have Bi'ah with not at the time of the Veses. He is not concerned lest she is Nidah.

Question (Rosh 1:1): Why is one's wife permitted when he returned from a journey? We expound (Shevu'os 18b) that one must refrain from his wife one Onah (here this means a day (morning to evening) or night) before her Veses, and all the more so if the Veses passed, one must be concerned lest she saw!

Answer (Rosh): We must say that it is long enough after the Veses that she could have immersed, like R. Yochanan discussed calculating the days of her Veses. This is only if Vestos mid'Rabanan. If Vestos mid'Oraisa, even if he waited enough for her to immerse, she is forbidden. It is as if he Vadai saw, so a Safek does not uproot a Vadai. Also the She'altos and R. Chananel said so. Also, we hold like R. Yehoshua against R. Eliezer, and like Chachamim against R. Meir. Also, Ravina is Basra, and he struggled to explain that Rebbi and R. Shimon ben Gamliel agree that Vestos mid'Rabanan.

Poskim

Shulchan Aruch (YD 184:11): If a woman has a Veses based only on days, if the Veses came, her husband may not have Bi'ah with until he asks her. If she has no Veses, day 30 from her last sighting is like her Veses.

Beis Yosef (DH v'Hashta): The Tur forbids until he asks her. This is when there was not enough time for her to immerse after the Veses. Even though Vestos mid'Rabanan, she is forbidden because usually the blood comes in its time.

Shach (30): He need not ask her before her Veses, or within 30 days if she has no Veses.

Pischei Teshuvah (27): Even if she is awake and lies next to him, he must ask her and she must say with her mouth that she is Tehorah.

Shulchan Aruch (ibid.): If enough days passed after the Veses for her to count and immerse, he may have Bi'ah with her without asking.

Beis Yosef (DH ha'Ba): Rav Huna holds that if her Veses came, even if he waited enough for her to immerse, she is forbidden, for Vestos mid'Oraisa. The Rashba explains that we consider it as if he Vadai saw, so she is forbidden until she says 'I am Tehorah.' Rabah bar bar Chanah permits, i.e. if there was enough for her to immerse. This is like his Rebbi, R. Yochanan.

Beis Yosef (DH u'Mah she'Chasav Bein Im Hi): Tosfos (12a DH Bein) says that there is no Isur Nidah, but one may not have Bi'ah with a sleeping woman, like it says in Nedarim.

Shach (31): Tosfos says that she is not totally asleep, for then Bi'ah is forbidden even without concern for Nidah.

Beis Yosef (DH veha'Rambam): The Magid Mishneh says that the Rambam explains that the Heter for one who came from a journey is only if she has a Veses. Reish Lakish and Rabah bar bar Chanah permit after the Veses, even without time to immerse. R. Yochanan requires time to immerse. The Halachah does not follow him. It seems that the Rif agrees. He did not distinguish whether or not the Veses came. The Ran says that this is an excessive leniency.