Imam Aḥmad based his argument on the ḥadith of Abū Hurayrah reported in the two Ṣaḥīḥ collections, in which the Prophet ﷺ said: “None of you should pray in a single garment if nothing of it covers his shoulders.”

The majority of scholars, however, regard the prohibition in this ḥadith as one of recommendation rather than absolute obligation. They also cite the fact that the Prophet ﷺ once prayed in a single garment, one end of which was draped over one of his wives while she was asleep. And Allah knows best.

Note
The well-known view in the Ḥanbalī school is that covering at least one shoulder is required only for the obligatory prayer. In supererogatory prayers it suffices to cover the ʿawrah, while covering both shoulders—or at least one of them—is recommended.

The reason for distinguishing between obligatory and voluntary prayers is that voluntary prayers are built on ease: one may omit standing, and while travelling may pray on a mount without facing the qiblah. Their rulings are therefore lighter than those of the obligatory prayer.

A second report from Imām Aḥmad, however, treats voluntary prayers the same as obligatory ones.

Al-Sharḥ al-Kabīr states: “The apparent wording of Imām Aḥmad indicates equality between the two, for whatever is stipulated for the obligatory prayer is likewise stipulated for the voluntary, and because the ḥadith is general with respect to both.” The same understanding is found in the words of our late teacher—may Allah have mercy on him.

Among those who adopted this view was our shaykh ʿAbd al-Raḥmān al-Saʿdī, who said: “The correct position is that covering the shoulder is the same for both obligatory and voluntary prayers; it is a sunnah in each of them and perfects one’s covering.”