حَدَّثَنَا الْقَعْنَبِيُّ، عَنْ مَالِكٍ، قَالَ لاَ بَأْسَ بِالدُّعَاءِ فِي الصَّلاَةِ فِي أَوَّلِهِ وَأَوْسَطِهِ وَفِي آخِرِهِ فِي الْفَرِيضَةِ وَغَيْرِهَا ‏.‏

Malik said: There is no harm in uttering supplication in prayer, in its beginning, in its middle, and in the end, in obligatory prayer or other. Translation Not Available

Book Ref: Sunan Abi Dawud Book 2 Hadith 769
Web Ref:  Sunan Abi Dawud Book 2 Hadith 768