Classical example of misreading and misunderstanding a hadith or taking your (own) understanding directly from the texts of the Sunnah of the Prophet (s.a.w.s.)
In a hadith in the Sunan of imam Tirmidhi we can read the Prophet (s.a.w.s.) prohibited sadl in salat. There you have proof the Malikis who pray with sadl got it all wrong! The Prophet s.a.w.s. clearly said it and the word is there litterally in the hadith (we can imagine someone saying). What clearer proof do you want? Brother/sister, can you go wrong reading this single hadith! How you might wonder?
1.) There are more ahadith on this subject, reading these will clarify to you what the Prophet (s.a.w.s.) meant exactly. See here: http://sunnah.com/search/?q=%D8%B3%D8%AF%D9%84 Always look at a hadith in perspective of other relevant ahadith on the same subject. Rulings are not established on a single hadith. Making up rulings after reading a hadith is wrong.
2.) Check an Arabic dictionary for the meaning of sadl, like the one of Hans Wehr for example, where we can read the verb sadala (or saddala) refers to letting something hang down, fall down, drop or to lower something. A sidl or a sudl is a veil or a curtain.
Knowing some Arabic is fundamental for understanding what you read.
3.) Sadl is specifically an issue in Maliki fiqh and thus the word also has a fiqhi or technical meaning instead of the linguistical meaning, although they are related. If you are not familiar with this issue you have a lot to learn still.
4.) In the hadith we read in the Sunan of imam Tirmidhi it refers to a prohibition of trailing the garments (like for a example the ‘abbayah or jalabiyyah) in prayer and not to the position of the arms in prayer as is known from Maliki fiqh texts like al-Murshid al-Mu’in. In that text it has been stated explicitly it is mandub (recommended) to let your arms hang down your sides in prayer. This is called sadl.
5.) Read the hadith with a teacher who will explain it to you or ask a teacher after you have read a hadith about the meaning.
6.) Taking your ‘knowledge’ directly from the sources without a teacher is not the way to learn and study. You will misread and misunderstand the Qur’an and the Sunnah.
To conclude: So to let your garments trail in the prayer (not the ‘imamah though!) is prohibited but not to let your arms hang down in the prayer.