The mitzvah of kindling Chanukah lamps is very dear. A person should be very careful in its observance to publicize the miracle and thus increase our praise of God and our expression of thanks for the miracles which He wrought on our behalf. Even if a person has no resources for food except [what he receives] from charity, he should pawn or sell his garments and purchase oil and lamps to kindle them [in fulfillment of the mitzvah]
Although the Rambam's ruling is accepted by all authorities, the commentaries question the Rambam's source. The Maggid Mishneh explains that since in Hilchot Chametz UMatzah 7:7 (based on Pesachim 10:1), the Rambam states that even a person who derives his income from charity should not drink less than four cups of wine on Pesach, we can conclude that the same concept applies with regard to Chanukah. Indeed, as explained in the following halachah, kindling Chanukah candles receives priority over the recitation of Kiddush. The concept of selling or pawning one's clothes to perform a mitzvah is mentioned in Megillah 27b with regard to the mitzvah of Kiddush.
When a person has only a single prutah and he [is required to fulfill both the mitzvot of] sanctifying the [Sabbath] day and lighting the Chanukah lamp, he should give precedence to purchasing oil to kindle the Chanukah lamp over [purchasing] wine to recite kiddush. Since both [of these mitzvot] are Rabbinic in origin, it is preferable to give precedence to the kindling of the Chanukah lamp, for it commemorates the miracle.
(יד) היה לפניו נר ביתו ונר חנוכה או נר ביתו וקדוש היום נר ביתו קודם משום שלום ביתו שהרי השם נמחק לעשות שלום בין איש לאשתו. גדול השלום שכל התורה ניתנה לעשות שלום בעולם שנאמר דרכיה דרכי נעם וכל נתיבותיה שלום
(14) 14 Someone had a light for his house or light for chanuka, or a light for his house or for the sanctification of the day; the light for the house come first for the sake of peace in the home. For surely God is erased in order to make peace between a husband and wife. Great is the peace for all of the Torah was given in order to make peace in the world as it says; her ways are the ways of pleasantness and all her paths are that of peace.
English from Judaica Press via Chabad.org