(123) باب مَا يُسْتَفْتَحُ بِهِ الصَّلاَةُ مِنَ الدُّعَاءِ
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.
Reference: Sunan Abi Dawud 769
In-book reference: Book 2, Hadith 379
English translation: Book 2, Hadith 768