Hadithcore
Musnad Ahmad, 330
da’if· Darussalam

It was narrated from Nafi’ that ‘Umar added to the mosque the area between the pillar and the enclosure, and ‘Uthman added[|something to the mosque], `Umar said:

Were it not for the fact that I heard the Messenger of Allah (ﷺ) say. `We want to extend our mosque,” I would not have added anything to it.

حَدَّثَنَا حَمَّادٌ الْخَيَّاطُ، حَدَّثَنَا عَبْدُ اللَّهِ، عَنْ نَافِعٍ، أَنَّ عُمَرَ، رَضِيَ اللَّهُ عَنْهُ زَادَ فِي الْمَسْجِدِ مِنْ الْأُسْطُوَانَةِ إِلَى الْمَقْصُورَةِ وَزَادَ عُثْمَانُ رَضِيَ اللَّهُ عَنْهُ وَقَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ لَوْلَا أَنِّي سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَقُولُ نَبْغِي نَزِيدُ فِي مَسْجِدِنَا مَا زِدْتُ فِيهِ‏.‏

References1 variant
In-Book Reference
Book 2, Hadith 236