Talmud for Ketubot 4:10
לֹא כָתַב לָהּ, בְּנִין דִּכְרִין דְּיֶהֱווֹן לִיכִי מִנַּאי אִנּוּן יִרְתוּן כְּסַף כְּתֻבְּתִיךְ יָתֵר עַל חוּלְקֵיהוֹן דְּעִם אֲחוּהוֹן, חַיָּב שֶׁהוּא תְנַאי בֵּית דִּין:
(If he did not write:) "You will sit in my house and be fed from my property all the days of the duration of your widowhood in my house," he is (nevertheless) liable (for this), for this is a condition of beth-din. The men of Jerusalem would write thus. The men of the Galil would write as the men of Jerusalem. The men of Judah would write: "…until the heirs desire to give you your kethubah." Therefore, if the heirs wish, they give her her kethubah and "exempt" her. [The halachah is not in accordance with the men of Judah; but so long as she does not marry and does not claim her kethubah in beth-din, she is fed from her husband's property, and lives in the house she lived in when her husband was alive, and uses all the vessels she used in her husband's lifetime.]