The ruling on performing Ḥajj during the waiting period (ʿiddah)

Answer—and Allah is the Granter of success: Here two obligations conflict for the woman in a way that she cannot combine them. What appears to me—and Allah knows best—is that it is permissible for her to perform Ḥajj even if some of the waiting period remains. The reasons:
1. The obligation of Ḥajj is a pillar among the five pillars of Islam; the obligation of ʿiddah is not of that rank.
2. The obligation of Ḥajj is a right of Allah the Exalted, whereas ʿiddah is a right of a human being; and Allah’s right has priority and precedence. Proof: “The debt owed to Allah has greater right to be discharged.”
3. There is no disagreement about the obligation of Ḥajj when its causes are present; it is a definitive obligation. By contrast, the requirement that the widow remain in a specific dwelling is a presumptive ruling.
4. It is narrated that the Commander of the Faithful—peace be upon him—performed Ḥajj with one of his daughters while she was in her waiting period due to her husband’s death.
5. The scholars of the madhhab have permitted the widow to go out for her needs—indicating that the occurrence of a need is an excuse for her going out; and there is no greater excuse than performing a pillar of Islam.
If it be said: The time for Ḥajj is expansive—the whole of one’s lifetime—so Ḥajj is not constricted to that year, unlike ʿiddah,
We say: The view that obligations are to be performed Ê immediately is the stronger—especially regarding Ḥajj—because of the long interval between its seasons. It is far-fetched for one who delays Ḥajj to presume he will live until the next year—or years—particularly for one advanced in age, as mentioned.
What indicates immediacy in Ḥajj is the ḥadīth, “Perform Ḥajj before you are unable to perform Ḥajj,” and the saying of Allah the Exalted: “Race to forgiveness from your Lord …” [Āl ʿImrān:133]. Delaying it exposes one to the threat and ruin mentioned in the ḥadīth: “Whoever dies without having performed Ḥajj—let him die, if he will, as a Jew or as a Christian,” and in His saying, Exalted is He: “And [due] to Allah from the people is a pilgrimage to the House—for whoever is able to find thereto a way. And whoever disbelieves—then indeed, Allah is free of need of the worlds.”  [ĀlʿImrān:97].
There is no doubt that one who was able to perform Ḥajj and yet did not, and then died, is exposed to threat and ruin—unless he meets Allah with a clear excuse.
If it be said: The occurrence of ʿiddah for the woman is a clear excuse to delay Ḥajj,
We say: ʿIddah is not an excuse to delay or leave Ḥajj. The Law has established that a husband is not permitted to prevent his wife from performing her obligatory Ḥajj, nor from an obligatory fast, and the like—even if that would deprive the husband of many of his rights or cause him hardship. This is evidence that the husband’s rights fall away when the obligations of Allah are at hand; and the waiting period due to death is of the same genus as the husband’s rights.
If it be said: The right implicated in the waiting period after death may be greater than the husband’s normal rights, so it is invalid to analogize it to those rights,
We say: It is not greater—proof being that it branches from, and is predicated upon, the husband’s rights; the branch cannot exceed the root. Nor is the sanctity of the dead greater than the sanctity of the living.
Yes: the widow’s obligations in ʿiddah due to death are:
1. Intending the ʿiddah;
2. Waiting for four months and ten days;
3. Observing mourning by refraining from adornment;
4. Remaining in the place where the news [of the death] reached her.
If she performs Ḥajj, only the last of these is missed; the first three are not incompatible with traveling for Ḥajj.
Moreover, in al-Shifāʾ it is reported from the Commander of the Faithful—peace be upon him—that he would have the widow transported to her home whenever she wished; and from him—peace be upon him—also: “The widow in her waiting period may observe her ʿiddah wherever she wishes—her home or her husband’s home.”
And from al-Qāsim, raising it to the Commander of the Faithful, likewise; and from Ibn ʿAbbās, likewise; and from ʿĀʾishah—that she moved her sister when her husband Ṭalḥah b. ʿUbayd Allāh al-Khuzāʿī was killed—and none of the Companions objected. All of this is cited in al-Shifāʾ.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1