بُلُوغُ الْمَرَامِ
Bulugh al-Maram 218
The Book of Prayer
وَعَنْ أَبِي سَعِيدٍ - رضى الله عنه - قَالَ : قَالَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -{ إِذَا جَاءَ أَحَدُكُمْ اَلْمَسْجِدَ , فَلْيَنْظُرْ, فَإِنْ رَأَى فِي نَعْلَيْهِ أَذًى أَوْ قَذَرًا فَلْيَمْسَحْهُ , وَلْيُصَلِّ فِيهِمَا } أَخْرَجَهُ أَبُو دَاوُدَ , وَصَحَّحَهُ اِبْنُ خُزَيْمَةَ [1]
Narrated Abu Sa'id (RA): Allah's Messenger (ﷺ) said: "When any of you comes to the mosque he should look and if he sees impurity on his sandals (shoes) he should wipe them and then pray in them." [Reported by Abu Dawud, and Ibn Khuzaimah graded it Sahih (authentic)].
Sunnah.com reference: Book 2, Hadith 82