A person can only give what is in his possession
A person can only give or bequeath what he actually owns.
("What they had in promissory notes at the time of the gift, you did not acquire, because the loan was given to be spent, and a person cannot give except what is in his possession" - Responsa Rashba, Part III, Siman 114)
Translation
Expression (Hebrew)
אֵין אָדָם יָכֹל לִתֵּן אֶלָּא מָה שֶּׁהוּא בִּרְשׁוּתוֹ
Definition (Hebrew)
אָדָם יָכוֹל לְהַעֲנִיק אוֹ לְהוֹרִישׁ רַק אֶת מָה שֶׁיֵּשׁ בְּבַעֲלוּתוֹ.
("מָה שֶׁהָיָה לָהֶם בְּשִׁטְרֵי חוֹב בִּשְׁעַת הַמְתָּנָה, לֹא קְנִיתֶם, שֶׁהַמַּלְוֶה לַהוֹצָאָה נִתְּנָה, וְאֵין אָדָם יָכוֹל לִתֵּן אֶלָּא מָה שֶׁהוּא בִּרְשׁוּתוֹ"- שׁוּ"ת הָרַשְׁבָּ"א חֵלֶק ג סִימָן קיד)