Yahya related to me from Malik from Abu'z Zinad from al-Araj from Abu Hurayra that the Messenger of Allah ﷺ said, "When you lead people in the prayer, make it short, because there are among them some people who are weak, ill and old. But when you pray on your own, make it as long as you wish."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِذَا صَلَّى أَحَدُكُمْ بِالنَّاسِ فَلْيُخَفِّفْ فَإِنَّ فِيهِمُ الضَّعِيفَ وَالسَّقِيمَ وَالْكَبِيرَ وَإِذَا صَلَّى أَحَدُكُمْ لِنَفْسِهِ فَلْيُطَوِّلْ مَا شَاءَ  

Yahya related to me from Malik that Nafi said, "I stood behind Abdullah ibn Umar in one of the prayers when there was no one else with him, and he reached behind with his hand and placed me beside him."  

أَنَّهُ قَالَ قُمْتُ وَرَاءَ عَبْدِ اللَّهِ بْنِ عُمَرَ فِي صَلاَةٍ مِنَ الصَّلَوَاتِ وَلَيْسَ مَعَهُ أَحَدٌ غَيْرِي فَخَالَفَ عَبْدُ اللَّهِ بِيَدِهِ فَجَعَلَنِي حِذَاءَهُ