وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ ابْنَ عُمَرَ، لَمْ يَكُنْ يَلْتَفِتُ فِي صَلاَتِهِ ‏.‏

Yahya related to me from Malik from Nafi that Ibn Umar wouldnever turn around when praying. Translation Not Available

Book Ref: Muwatta Imam Malik Book 9 Hadith 396
Web Ref:  Muwatta Imam Malik Book 9 Hadith 65