I reply: The plain sense of the verse to which al-Nawawī (may Allah have mercy on him) referred—Allah’s words in Sūrat al-Tawbah, “A mosque founded upon God-consciousness from the very first day is more deserving that you stand therein; in it are men who love to purify themselves, and Allah loves those who purify themselves” (9:108)—points to the mosque of Qubāʾ. The verse contains two pronouns that, by unanimous agreement, refer back to a single antecedent, and the pronoun attached to the circumstantial phrase that introduces “men who love to purify themselves” clearly refers to the mosque of Qubāʾ. Hence, it is that mosque which was founded on God-fearingness. The proof is the occasion of revelation.

Aḥmad narrated (3/422) through the route of Abū Uways: Sharaḥbīl related from ʿUwaym ibn Sāʿidah al-Anṣārī, who said:

“The Prophet ﷺ came to us in the mosque of Qubāʾ and said, ‘Allah, the Blessed and Exalted, has praised you for the purification connected with your mosque. What is this purification by which you cleanse yourselves?’ They replied, ‘By Allah, O Messenger of Allah, we know nothing other than that we had neighbors from the Jews who used to wash their backsides after relieving themselves, so we washed as they washed.’”

Its chain is fair. Ibn Khuzaymah also recorded it in his Ṣaḥīḥ, as cited in Ibn Kathīr’s Tafsīr (2/389).

There is another supporting report with a fair chain as well, recorded in Naṣb al-Rayah (1/219) from the narrations of Abū Ayyūb al-Anṣārī, Jābir ibn ʿAbd Allah, and Anas ibn Mālik. Ibn Mājah produced it (1/146), as did al-Ḥākim (2/334–335), who declared, “Its chain is sound,” and al-Dhahabī concurred.