Answer

Assalaam alaykum wa Rahmatullahi wa barakatuh My questions is in regards to Salat, I wanted to know what is the shafi position with praying on/with khumrah? Is it considered mustahab or fard? I was reading some Hadith about it and heard some scholars say it is a clay tablet like our Shia brothers pray with. Also I wanted to know if there is a book that list the Hadith for the closing of hands in salah? Which position is most correct according to the sunnah of Rasulullah(SAWS). Jazakallah khair in advance for all your assistance. May Allah reward you for your efforts

Walaykumusalaam warahmatullahi wabarakaatuh,

Definition of a Khumrah

"It is a small mat made from palm leaves. It was named 'khumrah' because it covers the face and hands from the extreme heat or cold of the ground, if it were bigger,  it is called 'haseer'."¹

Praying on a Khumrah

Imam Nawawi says regarding the narrations in which the prophet (peace be upon him) prayed on haseer:

"There is evidence in it for the permissibility of praying on something between him [the worshipper] and the ground whether it is made from fabric,  palm leaves, wool,  fur,  and others, regardless of it coming from the earth or not."²

Regarding the question of whether it is sunnah to hold one's hands in salah (qabdh) or to drop them to one's side (sadl): 
It is an area of disagreement amongst the mujtahid imams and each one has his supporting evidence. Our obligation, my dear brother/sister, is simply to follow one of the four sunni mujtahid imams. We are not required to search for the one with the strongest dalil.³ 
Also, debate and argumentiaon over these matters is frowned upon by the Shariah. We should, instead,  invest our precious time in learning the obligatory religious instruction and apply it in our lives to the best of our ability. It was said by one of the early predecessors,

"There will be at the end of time people for whom the door of works will be closed,  and the door of argumentaion opened."⁴

May Allah (the Exalted) make us from those for whom the doors of good works will be opened.

[1] Fath-ul-bari 1/430
[2] Sharh Muslim 4/233,234
[3] al-'Iqd al-Fareed 65
[4] Qut al-Qulub 1/138

Answered by: Shaykh Omar Mohsin