Prophet said (to two persons), "Whenever the prayer time becomes due, you should pronounce Adhan and then Iqama and the older of you should lead the prayer." (Using translation from Bukhārī 658)   

أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا حَضَرَتِ الصَّلَاةُ فَأَذِّنَا ثُمَّ أَقِيمَا ثُمَّ لِيَؤُمَّكُمَا أَكْبَرُكُمَا  

I came to the Messenger of Allah ﷺ along with a companion of mine, and when we intended to return from him, he said: When there is time for prayer, announce prayer, pronounce Iqama, and the oldest amongst you should lead the prayer. (Using translation from Muslim 674d)   

أَتَيْتُ النَّبِيَّ ﷺ أَنَا وَصَاحِبٌ لِي فَلَمَّا أَرَدْنَا الْإِقْفَالَ مِنْ عِنْدِهِ قَالَ لَنَا إِذَا حَضَرَتِ الصَّلَاةُ فَأَذِّنَا ثُمَّ أَقِيمَا وَلْيَؤُمَّكُمَا أَكْبَرُكُمَا  

[Machine] The Messenger of Allah ﷺ led us in the Fajr prayer and said, "Do you bear witness to so-and-so?" They said, "No." He said, "Do you bear witness to so-and-so?" They said, "No." He said, "Indeed, these two prayers, meaning the 'Isha and Fajr prayers, are the heaviest prayers on the hypocrites. If they knew their virtues, they would come to them even if they had to crawl. And the first row is like the row of angels, and if you knew its virtue, you would compete to be in it. And the prayer of a man with another man is purer than his prayer alone, and his prayer with two men is purer than his prayer with one man. And the more it increases, the more beloved it is to Allah." Like this.  

صَلَّى بِنَا رَسُولُ اللهِ ﷺ صَلَاةَ الصُّبْحِ فَقَالَ أَشَاهِدٌ فُلَانٌ؟ قَالُوا لَا قَالَ أَشَاهِدٌ فُلَانٌ؟ قَالُوا لَا قَالَ إِنَّ هَاتَيْنِ الصَّلَاتَيْنِ يَعْنِي الْعِشَاءَ وَالصُّبْحَ مِنْ أَثْقَلِ الصَّلَاةِ عَلَى الْمُنَافِقِينَ وَلَوْ يَعْلَمُونَ مَا فِيهِمَا لَأَتَوْهُمَا وَلَوْ حَبْوًا وَالصَّفُّ الْأَوَّلُ عَلَى مِثْلِ صَفِّ الْمَلَائِكَةِ وَلَوْ تَعْلَمُونَ فَضِيلَتَهُ لَابْتَدَرْتُمُوهُ وَصَلَاةُ الرَّجُلِ مَعَ الرَّجُلِ أَزْكَى مِنْ صَلَاتِهِ وَحْدَهُ وَصَلَاتُهُ مَعَ الرَّجُلَيْنِ أَزْكَى مِنْ صَلَاتِهِ مَعَ الرَّجُلِ وَمَا كَثُرَ فَهُوَ أَحَبُّ إِلَى اللهِ ﷻ هَكَذَا  

The Messenger of Allah ﷺ saw a person praying alone. He said: Is there any man who may do good with this (man) and pray along with him. (Using translation from Abū Dāʾūd 574)   

أَنَّ النَّبِيَّ ﷺ أَبْصَرَ رَجُلًا يُصَلِّي وَحْدَهُ فَقَالَ أَلَا رَجُلٌ يَتَصَدَّقُ عَلَى هَذَا فَيُصَلِّي مَعَهُ؟  

[Machine] The Messenger of Allah ﷺ said, "There are two, and above them is a congregation."  

قَالَ رَسُولُ اللهِ ﷺ اثْنَانِ فَمَا فَوْقَهُمَا جَمَاعَةٌ كَذَلِكَ  

[Machine] The Messenger of Allah ﷺ said: "A man has the right to the breast of his riding animal, and a man has the right to the breast of his bed." He said: "The two are a group, and the three are a group, and whatever is more is a group."  

قَالَ رَسُولُ اللهِ ﷺ الرَّجُلُ أَحَقُّ بِصَدْرِ دَابَّتِهِ وَالرَّجُلُ أَحَقُّ بِصَدْرِ فِرَاشِهِ قَالَ قَالَ رَسُولُ اللهِ ﷺ الِاثْنَانِ جَمَاعَةٌ وَالثَّلَاثَةُ جَمَاعَةٌ وَمَا كَثُرَ فَهُوَ جَمَاعَةٌ