Mishkat al-Masabih 1129
Anas said:
I never prayed behind an imam , who was more brief or more perfect in his prayer than the Prophet. If he heard a boy crying he would shorten the prayer for fear his mother might be distressed. 

(Bukhari and Muslim.)
عَنْ أَنَسٍ قَالَ: مَا صَلَّيْتُ وَرَاءَ إِمَامٍ قَطُّ أَخَفَّ صَلَاةً وَلَا أَتَمَّ صَلَاةً مِنَ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَإِنْ كَانَ لَيَسْمَعُ بُكَاءَ الصَّبِيِّ فَيُخَفِّفُ مَخَافَةَ أَنْ تُفْتَنَ أمه