WEARING CAP IN SALAAT PART -1

To cover the head, using a turban or wearing a skull cap (Topi) is Sunnah.  The Holy Prophet (Sallallahu alaihi wa sallam) would tie a turban on the cap.  Imam Haithami has established a chapter on "Topi" in his book of Hadith Majma Uz Zawaaid and has recorded a Hadith on the authority of Tabarani:

Translation of Hadith:  It has been narrated on the authority of Hadhrat Abdullah bin Umar (May Allah be well pleased with them) that the Holy Prophet (Sallallahu alaihi wa sallam) would wear a white cap.  

(Majma Uz Zawaaid, Vol. 5, Pg No. 121)

There is a Hadith in Jame' Tirmidhi:

Translation of Hadith:  Indeed! The difference between us and the "Mushrikeen" (those who take partners with Allah Ta'ala) is turbans tied on caps.  

(Jame' Tirmidhi, Vol. 1, Pg No. 308)