Does the verse on hijab in Surat al-Ahzab: "And when you ask [his wives] for something, ask them from behind a partition (hijab)," abrogate the fact that the wives of the Prophet are Mothers of the Believers, such that it is inconceivable for mothers to observe hijab from their sons?

The wives of the Prophet, peace and blessings be upon him, are the Mothers of the Believers in terms of the prohibition of marrying them after his death and their deserving of respect, veneration, and honor. This status does not, however, imply a degree of mahramiyyah (unmarriageability) that would permit the uncovering of the hijab. Thus, there is no contradiction between the two verses in Surah Al-Ahzab, and they are obligated to observe hijab in front of those who are not their mahrams.