The Prophet (may Allah's peace and blessings be upon him) would visit the mosque of Qubā' riding or walking, then he would pray there two Rak‘ahs
Authentic hadithعن عبد الله بن عمر رضي الله عنهما قال: كان النبي صلى الله عليه وسلم يزورُ قُبَاءَ راكبًا وماشيًا، فيُصَلِّي فيه ركعتين. وفي رواية: كان النبي صلى الله عليه وسلم يأتي مسجد قُبَاءَ كل سَبْتٍ راكبًا وماشيًا، وكان ابن عُمر يفعله.
Abdullāh ibn ‘Umar (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) would visit the mosque of Qubā riding or walking, then he would pray there two Rak‘ahs. In another narration: "The Prophet (may Allah's peace and blessings be upon him) would go to the mosque of Qubā every Saturday riding or walking, and Ibn ‘Umar would do so as well.
Explanation
The Qubā' region, where the first mosque of Islam was built, is a town near the center of Madīnah in its ‘Awāli district. The Prophet would visit this place either riding or walking. The words "every Saturday" means that he would designate certain days for visiting it. The wisdom behind him visiting Qubā' on Saturday of every week was to maintain relations with the Ansāris and to see how they were doing, as well as those who stayed behind of attending the Friday prayer with him. This is the reason why the Prophet (may Allah's peace and blessings be upon him) designated Saturday for their visit.
Source · Al-Bukhari and Muslim with its two versions
From the Hadith Encyclopedia (hadeethenc.com).