Bava Batra

[One] master  holds the opinion [that Raba's meaning was that the sale] of a part  [only of the estate was] invalid, and the [other] Master  holds the opinion [that Raba's meaning was that] the entire [sale was invalid]. [A message] was sent from Palestine:  [If] a firstborn son had sold [his share] before the division [of the estate took place, that sale] is invalid.  This shows that the firstborn is not regarded as the [legal] possessor of his share  before distribution [had taken place]. And the law is that the firstborn is the possessor of his share  [even] before distribution [of the estate had taken place]. Mar Zutra of Darishba divided a basket  of pepper with [his] brothers in equal [shares].  [When] he came before R. Ashi, [the latter] said to him: 'Since you have renounced [your rights in] a part [of the estate]  you have [implicitly] renounced [them] in all of it'. MISHNAH. [IF] ANY ONE SAID,  'MY FIRSTBORN SON, SHALL NOT RECEIVE A DOUBLE PORTION,' [OR] 'X, MY SON, SHALL NOT BE HEIR WITH HIS BROTHERS', HIS INSTRUCTIONS ARE DISREGARDED,  BECAUSE HE MADE A STIPULATION [WHICH IS] CONTRARY TO WHAT IS WRITTEN IN THE TORAH.  IF ONE  DISTRIBUTED HIS PROPERTY VERBALLY, [AND] GAVE TO ONE [SON] MORE, AND TO [ANOTHER] ONE LESS, OR [IF] HE ASSIGNED TO THE FIRST BORN A SHARE EQUAL TO THAT OF HIS BROTHERS,  HIS ARRANGEMENTS ARE VALID.  IF, [HOWEVER], HE SAID, AS AN INHERITANCE',  HIS INSTRUCTIONS ARE DISREGARDED.  [IF] HE WROTE,  EITHER AT THE BEGINNING OR THE MIDDLE OR THE END, 'AS A GIFT',  HIS INSTRUCTIONS ARE VALID. GEMARA. [Must] it be said [that] our Mishnah  is not in accordance with R. Judah? For, if [it be suggested that it is in accordance with] R. Judah. surely he said, [it may be asked]. [that] in money matters one's stipulation is valid'.  For it was taught: If a man said to a woman, 'Behold thou art consecrated unto me  on condition that thou shalt have no [claim] upon me [for] food, raiment and conjugal rights' she is consecrated  but the stipulation is null;  these are the words of R. Meir. R. Judah said: In respect of the money matters his stipulation is valid!  [Our Mishnah] may be said [to be in agreement] even [with the view of] R. Judah; [only] there,  she knew [his conditions] and renounced her privilege  [but] here,  [the son] did not renounce [his privileges]. R. Joseph said: [If] one said, 'X is my firstborn son', [the latter] is to receive a double portion.  [But if he said]. 'X is a firstborn' [the latter] is not to receive a double portion, for he may have meant,' the firstborn son of his mother'. A certain [person once] came before Rabbah b. Bar Hana [and] said to him, 'I am certain that this [man] is a firstborn'. He said to him: 'Whence do you know [this]?' 'Because his father called him foolish  firstborn' 'He might have been the firstborn of his mother [only], because the firstborn of a mother is also called foolish firstborn.' A certain [person once] came before R. Hanina [and] said to him, 'I am certain that this [man] is firstborn'. He said to him, 'Whence do you know [this]?' — [The other] replied to him: 'Because when [people] came to his father,  he used to say to them: Go to my son Shikhath, Who is firstborn and his spittle heals'. — Might he not have been the firstborn of his mother [only]? — There is a tradition that the spittle of the firstborn of a father is healing, but that of the firstborn of a mother is not healing. R. Ammi said: A tumtum  [firstborn] who, having been operated upon  was found to be a male, does not receive a double portion [as heir], for Scripture says. And if the firstborn son be hers that was hated,  [which implies that he cannot be regarded as firstborn] unless  he was a son at the beginning  of [his] being.  R. Nahman b. Isaac said: Neither is he tried as a 'stubborn and rebellious son';  for Scripture says, If a man have a stubborn and rebellious son,  [which implies that] he must have been  a son at the beginning  of[his] being.