Rif Moed Katan 16a {Moed Katan 26b; Yerushalmi Shabbat; Bavli Moed Katan 26b}

16a

{Moed Katan 26b}

ת"ר הקורע מתוך השלל ומתוך המלל מתוך הלקטן מתוך הסולמות לא יצא מתוך האיחוי יצא אמר רב חסדא ובאיחוי אלכסנדראי

The Sages learnt {in a brayta}: If one tears from that which had previously been joined in any of the baste, from the hemmed over area, from the gathering, from the ladder {see immediately above for definitions of each of these types of sewing something that has previously been torn} he has not fulfilled. From the sewing, he fulfilled.
Rav Chisda {once again} said: And specifically Alexandrian sewing {where the seam is invisible}.

ת"ר רשאי להפכו למטה ולאחותו ר"א בר"ש אוסר באיחוי
וקי"ל כותיה
וכשם שהמוכר אסור לאחותו כך הלוקח אסור לאחותו לפיכך מוכר צריך להודיע ללוקח
תניא ר' יוסי אומר תחלת קריעה טפח ומוסיף כל שהוא
והלכתא כוותיה

The Sages learnt {in a brayta}: He is permitted to wear it upside-down and to then sew it.
R' Eleazar beRabbi Shimon said: He is forbidden is sewing.
And we establish like him {R' Eleazar beRabbi Shimon}.

And just as the seller is forbidden to resew it, so is the buyer forbidden to resew it. Therefore the seller needs to inform the buyer.

They learnt {in a brayta}: Rabbi Yossi says: The beginning of a tear is one handbreadth, and when he adds, it is any amount.
And the halacha is like him.

ירושלמי בפרק יציאות השבת ישב לגלח ובאו ואמרו לו מת אביו ה"ז משלים אחד המגלח ואחד המתגלח

Yerushalmi, in perek Yetziot haShabbat - if he was sitting to shave {get a haircut} and they came and told him that his father died, he finishes, whether he was the barber or the one getting the cut.

גרסי' בסוף נדרים
תניא אמרו לו מת אביו וקרע ואח"כ נמצא שמת בנו יצא ידי קריעה
ותניא אחריתא אמרו לו מת אביו וקרע ואח"כ נמצא שמת בנו לא יצא ידי קריעה
אמרו לו מת לו מת וכסבור אביו היה וקרע ואח"כ נמצא בנו לא יצא ידי קריעה

ופריק רב אשי כאן בתוך כדי דיבור וכאן לאחר כדי דבור
הא דאמרת יצא ידי קריעה שנמצא בנו בתוך כדי דבור והא דאמרת לא יצא ידי קריעה לאחר כדי דבור

We learn at the end of Nedarim: They learnt {in a brayta}: If they told him that his father died and he tears, and afterwards it turns out that it was his son that died, he has fulfilled his obligation to tear.
And another brayta states: If they told him that his father died and he tears, and afterwards it turns out that it was his son that died, he has not fulfilled his obligation to tear. If they told him that some relative of his had died {not specifying} and he thought it was his father, and tears, and afterwards it turns out that it was his son that died, he has not fulfilled his obligation to tear.

And Rav Ashi resolves it as follows: Here was when it was {made clear} toch kedei dibbur {a short period of time that it takes to say, e.g. Shalom Alechem Rabbi uMori - which is the time people misspeak and then make corrections}, and this is after toch kedei dibbur. This that you stated that he has fulfilled his obligation to tear is where it came out that it was his son toch kedei dibbur, and this that you said that he has not fulfilled his obligation to tear is after kedei dibbur.

תניא מי שהיה לו חולה בתוך ביתו ונתעלף וכמדומה לו שמת וקרע ואח"כ מת לא יצא ידי קריעה

אמר ר"ש בן פזי א"ר יהושע בן לוי משום בר קפרא לא שנו אלא שמת לאחר כדי דיבור אבל בתוך כדי דיבור אין חוזר וקורע
וכן הלכתא

They learnt {in a brayta}: If someone has a sick person in his house, and he passed out and it appears that he died, and he tears, and afterwards the person actually dies, he has not fulfilled his obligation to tear.

Rabbi Shimon ben Pazi cited Rabbi Yehoshua ben Levi who cited bar Kappara: They only taught this where the person died after kedei dibbur, but toch kedei dibbur he does not return and rip.
And so is the halacha.

{Moed Katan 26b}

ת"ר אמרו לו מת אביו וקרע מת בנו והוסיף התחתון מתאחה העליון אין מתאחה
מת בנו וקרע מת אביו והוסיף עליון מתאחה תחתון אין מתאחה
מת אביו ומתה אמו מת אחיו ומתה אחותו קורע קרע אחד לכולן
ר"י בן בתירא אומר על כולן קורע קרע אחד על אביו ועל אמו קרע אחד לפי שאין מוסיפין על קרע של אביו ושל אמו

The Sages learnt {in a brayta}: If they told him that his father died and he tore, then that his son died and he adds {to the tear}, the bottom portion {for his son} may be resewn but the top portion may not be resewn. That his son died and he tears, that his father died and he adds {to the tear}, the top portion may be resewn and the bottom portion may not be resewn. That his father died and that his mother died and that his sister died, he tears a single tear for all of them {together}.
Rabbi Yehuda ben Beteira says: For each of them he tears - one tear for his father and one tear for his mother {and one for his sister} for they do not add to the tear for his father and for his mother.

מ"ט אמר רב נחמן בר יצחק לפי שאינן בתוספת
אמר שמואל הלכה כרבי יהודה בן בתירא
והאמר שמואל הלכה כדברי המיקל באבל
אבילות לחוד וקריעה לחוד

What is the reason?
Rav Nachman bar Yitzchak said: Because they are not amongst those for which one adds {thus, if he tears for his son, he may not simply add if he hears his father died as well}.
Shmuel said: The halacha is like Rabbi Yehuda ben Beteira.

But Shmuel said: The halacha is like the more lenient opinion by a mourner?! {So how could Shmuel say this here?}
General mourning is a separate topic from tearing.