Layth—namely, Ibn Abī Sulaym—is a weak transmitter, and Jabbārah ibn al-Mughallis is even weaker than he.
Ibn Mājah also narrates the report through this same Jabbārah, from ʿAbd al-Karīm ibn ʿAbd al-Raḥmān, from Abū Isḥāq, from ʿAmr ibn Maymūn, from ʿUmar ibn al-Khaṭṭāb in marfūʿ form. Fatḥ al-Bārī states: “Its men are trustworthy except for his shaykh Jabbārah ibn al-Mughallis; there is some criticism regarding him.” In al-Taqrīb al-Ḥāfiẓ writes: “He is weak.” For that reason Ibn Kathīr said, “Its chain is weak.”
Al-Khaṭṭābī explains in Maʿālim al-Sunan: “Tashyīd means to raise and lengthen a building.” Al-Baghawī says the same, as cited in Nayl al-Awtār, and adds: “The expression also appears in His words, ‘fortified towers’ (Q. 4:78), meaning structures whose construction has been made lofty. One says shadadtu al-shayʾ asheeduhu—like baʿtu abayʿu—meaning, ‘I built it with shīd,’ that is, with gypsum; and shayyadtu-hu tashyyīdā means, ‘I made it tall and elevated it.’”
Others have said that the “fortified towers” are those coated with plaster. Ibn Ruslān remarks: “The prevalent understanding of the hadith is that tashyīd of mosques here refers to elevating and elongating their structures, as al-Baghawī stated. This refutes those who interpret the verse, ‘In houses which Allah has allowed to