Arabic hadith text
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّهُ قَالَ إِنَّمَا أُنْزِلَتْ هَذِهِ الآيَةُ ‏{‏وَلاَ تَجْهَرْ بِصَلاَتِكَ وَلاَ تُخَافِتْ بِهَا وَابْتَغِ بَيْنَ ذَلِكَ سَبِيلاً‏}‏ فِي الدُّعَاءِ ‏.‏ قَالَ يَحْيَى وَسُئِلَ مَالِكٌ عَنِ الدُّعَاءِ فِي الصَّلاَةِ الْمَكْتُوبَةِ فَقَالَ لاَ بَأْسَ بِالدُّعَاءِ فِيهَا ‏.‏
Translation

Yahya related to me from Malik from Hisham ibn Urwa that hisfather said, "The following ayat was sent down about dua - 'And do notbe loud in your prayer and do not be silent in it, but seek a waybetween these.' " (Sura 17 ayat 110)

Yahya said that Malikwas asked about making dua in obligatory prayers and he said, "Thereis no harm in making dua in them."