Halakhah zu Bereschit 26:7

In point of fact, it appears to this writer that there does exist an alternate method not subject to the aforementioned objections and deficiencies. In every marriage, the husband, by virtue of the conditions of the ketubah and of rabbinic legislation, is obliged to provide for the needs of his wife. The style in which a husband is obligated to support his wife and the extent of this obligation are carefully spelled out in Shulḥan Arukh, Even haEzer 70:1–3. However, there is nothing to prevent the husband from voluntarily obligating himself to a more generous level of support. Rashi, Genesis 26:7, cites the midrashic comment which points out that the food brought by Jacob to his father was not stolen but was the lawful property of his mother. The Midrash declares that Isaac included a clause in Rebeccah's ketubah obligating him to provide her with a daily allowance of two goats.