كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5  
The Book of Mosques and Places of Prayer
(7)
Chapter: The prohibition of speaking during the prayer, and the abrogation of its former permissibility
(7)
باب تَحْرِيمِ الْكَلاَمِ فِي الصَّلاَةِ وَنَسْخِ مَا كَانَ مِنْ إِبَاحَتِهِ ‏
Sahih Muslim 540 c

Jabir reported:

We were in the company of the Messenger of Allah (ﷺ), and he sent me on an errand, and when I came back (I saw him) saying prayer on his ride and his face was not turned towards Qibla. I greeted him but he did not respond to me. As he completed the prayer, he said: Nothing prevented me from responding to your greeting but the fact that I was praying.
حَدَّثَنَا أَبُو كَامِلٍ الْجَحْدَرِيُّ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ كَثِيرٍ، عَنْ عَطَاءٍ، عَنْ جَابِرٍ، قَالَ كُنَّا مَعَ النَّبِيِّ صلى الله عليه وسلم فَبَعَثَنِي فِي حَاجَةٍ فَرَجَعْتُ وَهُوَ يُصَلِّي عَلَى رَاحِلَتِهِ وَوَجْهُهُ عَلَى غَيْرِ الْقِبْلَةِ فَسَلَّمْتُ عَلَيْهِ فَلَمْ يَرُدَّ عَلَىَّ فَلَمَّا انْصَرَفَ قَالَ ‏ "‏ إِنَّهُ لَمْ يَمْنَعْنِي أَنْ أَرُدَّ عَلَيْكَ إِلاَّ أَنِّي كُنْتُ أُصَلِّي ‏"‏ ‏.‏
Reference : Sahih Muslim 540c
In-book reference : Book 5, Hadith 47
USC-MSA web (English) reference : Book 4, Hadith 1102
  (deprecated numbering scheme)