كتاب الصلاة
4  
The Book of Prayers
(16)
Chapter: The Tashah-hud In The Prayer
(16)
باب التَّشَهُّدِ فِي الصَّلاَةِ ‏
Sahih Muslim 402 c

This hadith has been narrated on the authority of Mansur with the same chain of transmitters and he made a mention of this:

" Then he may choose any supplication which pleases him or which he likes."
حَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، حَدَّثَنَا حُسَيْنٌ الْجُعْفِيُّ، عَنْ زَائِدَةَ، عَنْ مَنْصُورٍ، بِهَذَا الإِسْنَادِ مِثْلَ حَدِيثِهِمَا وَذَكَرَ فِي الْحَدِيثِ ‏ "‏ ثُمَّ لْيَتَخَيَّرْ بَعْدُ مِنَ الْمَسْأَلَةِ مَا شَاءَ أَوْ مَا أَحَبَّ ‏"‏ ‏.‏
Reference : Sahih Muslim 402c
In-book reference : Book 4, Hadith 61
USC-MSA web (English) reference : Book 4, Hadith 795
  (deprecated numbering scheme)