According to the Salafis "it is not prescribed to place the hands over the face after finishing du’aa’."
However, this was the sunnah and practise of Rasulullah صلي الله عليه وسلم
عن عمر بن الخطاب رضي الله عنه قال : كان رسول الله صلى الله عليه و سلم إذا رفع يديه في الدعاء لم يحطهما حتى يمسح بهما وجهه
'Umar ibn al-Khattab (رضي الله عنه) reports: "When Rasulullah (صلي الله عليه وسلم) would raise his hands in du'a, he would not lower them until he passed them over his face." (Sunan Al-Tirmizhi, #3386)
Ibn Hajr Asqalani (رحمه الله) has classified the above Hadith as sound. (Bulugh Al-Muraam, pg 264, Dar Al-Fikr).
