Question
If I pray Zuhr in the 1st Mithl of Asr, if I finish the Zuhr farz salah into the time of the second Mithl, is it valid?
Answer:
ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﯿﻢ
In the name of Allah, the Most Gracious, the Most Merciful
The time of Zuhr commences when the sun declines from its zenith, and its time remains until the shadow of everything becomes twice its length, excluding the shadow of midday. Once the shadow of everything becomes twice its length (2 mithls), excluding the shadow of midday, Asr time begins. Based upon the above mentioned explanation, if you started your Zuhr Salah in its time, afterwards the Asr time enters (two mithls) whilst you were praying, then the prayer would be invalid and must be made up (qada).
Only Allah knows best
Written by Maulana Mohammad Ahsan Osmani Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
(Mukhtasar Al Quduri: p. 57-58 [Bushra]; Bahishti Zewar: p. 111)