Berakhot 18A

ואין מברכין עליו, ואין מזמנין עליו, ופטור מקריאת שמע ומן התפלה ומן התפילין ומכל מצות האמורות בתורה. ובשבת מיסב ואוכל בשר ושותה יין, ומברך ומזמן, ומברכין עליו ומזמנין עליו, וחייב בכל המצות האמורות בתורה. רבן שמעון בן גמליאל אומר: מתוך שנתחייב באלו ⁠— נתחייב בכולן.

And there is no need for others to recite a blessing beforehand on his behalf, nor do others invite him to join in Grace after Meals, as he cannot be a member of the quorum of 3 required to recite the formula. He is exempt from the recitation of Shema, from the Amida prayer and from tefillin, and from all mitzvot mentioned in the Torah. On Shabbat, however, he reclines at the meal as per his custom, and eats meat and drinks wine, and recites blessings and recites the formula to invite the participants in the meal to join together in the Grace after Meals, and others may recite blessings on his behalf and invite him to join in Grace after Meals, and he is obligated in all mitzvot mentioned in the Torah. Rabban Shimon ben Gamliel says: Just as he is obligated on Shabbat to fulfill these mitzvot associated with Shabbat meals, he is obligated to fulfill all mitzvot.

ואמר רבי יוחנן: מאי בינייהו ⁠— תשמיש המטה איכא בינייהו.

R' Yoḥanan said: What is the practical difference between the apparently identical statements of Rabban Shimon ben Gamliel and the first tanna? The practical difference between them is with regard to sex. The first tanna holds that although there is no mourning on Shabbat, since refraining from addressing his wife’s conjugal rights would not be a public display of mourning, sex are prohibited. Rabban Shimon ben Gamliel holds that since there is no mourning on Shabbat, he must fulfill the mitzva of addressing his wife’s conjugal rights.

קתני מיהת פטור מקריאת שמע ומן התפלה ומן התפילין ומכל מצות האמורות בתורה! אמר רב פפא: תרגמא אמחזיר פניו ואוכל. רב אשי אמר: כיון שמוטל עליו לקוברו, כמוטל לפניו דמי. שנאמר: ״ויקם אברהם מעל פני מתו״, ונאמר: ״ואקברה מתי מלפני״, כל זמן שמוטל עליו לקוברו כמוטל לפניו דמי.

In any event, the baraita teaches that one is exempt from the recitation of Shema, from the Amida prayer and from tefillin, and from all mitzvot mentioned in the Torah. This is an apparent contradiction of our Mishnah which states that one is exempt only when the deceased is laid before him. To resolve this contradiction, Rav Pappa said: Explain the baraita as applicable only to the particular case when one turns his face away and eats, with the deceased laid out before him. In the other cases, when he is in a different room, he is obligated in all mitzvot. Rav Ashi says: The phrase: The deceased is laid out before him, is not to be taken literally, but rather, since it is incumbent upon him to bury the deceased, and he is not yet buried, it is as if he is laid out before him, as it is stated: “And Abraham rose up from before his dead” (Genesis 23:3), and when Abraham speaks with the Hittites, it is stated: “So that I may bury my dead from before me” (Genesis 23:4). As long as it is incumbent upon him to bury him, it is as he is laid out before him.