Bava Batra 144 - Estate Division Must be Formalized
If a man died and left adult and minor sons, and the adults improved the estate, their improvements go to the common estate, since the estate was as yet undivided. However, if the adult sons said in court or some other public forum, "See what our father has left us," - that is, assess the total value and let us divide it, and "hereafter whatever improvements we make using the estate resources will be counted as done using our portion", the improvement accrues to them.
Rav Safra's father died and left money to Rav Safra and his minor brothers. Rav Safra did business with this money and realized profit. The brothers summoned him for adjudication before Rava, but Rava said, "Rav Safra is a Sage and a scholar. He would not stop his studies to work for others, so it is assumed that he worked for himself."
Art: Samuel de Wilde - Mr Bannister Junior and Mr Parsons as Scout and Sheepface in The Village Lawyer