Jabir b. Samura reported: 'Umar said to Sa'd: They complain against you in every matter, even in prayer. He (Sa'd) said: I prolong (standing) in the first two (rak'ahs) and shorten it in the last two, and I make no negligence in following the prayer of the Messenger of Allah (ﷺ). He ('Umar) remarked: This is what is expected of you, or, that is what I deemed of you.
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي عَوْنٍ، قَالَ سَمِعْتُ جَابِرَ بْنَ سَمُرَةَ، قَالَ عُمَرُ لِسَعْدٍ قَدْ شَكَوْكَ فِي كُلِّ شَىْءٍ حَتَّى فِي الصَّلاَةِ . قَالَ أَمَّا أَنَا فَأَمُدُّ فِي الأُولَيَيْنِ وَأَحْذِفُ فِي الأُخْرَيَيْنِ وَمَا آلُو مَا اقْتَدَيْتُ بِهِ مِنْ صَلاَةِ رَسُولِ اللَّهِ صلى الله عليه وسلم . فَقَالَ ذَاكَ الظَّنُّ بِكَ . أَوْ ذَاكَ ظَنِّي بِكَ .
sunnah.com