Yahya related to me from Malik from Hisham ibn Urwa that his father said, "The following ayat was sent down about dua - 'And do not be loud in your prayer and do not be silent in it, but seek a way between these.' " (Sura 17 ayat 110) Yahya said that Malik was asked about making dua in obligatory prayers and he said, "There is no harm in making dua in them."