Is it permissible to begin a non-causal voluntary prayer outside the prohibited times?
Chapter on the Times When Prayer is Prohibited
Al-Mughni
Book of Prayer
Primary text
It is not permissible to intentionally begin a voluntary prayer that is not related to a specific cause (Sabab) if it falls outside the period of prohibition after Fajr or Asr. The established view among those who prohibit prayer after Asr is that commencing voluntary prayer is generally restricted.
Supporting text
A group of early scholars permitted voluntary prayer after Asr, citing the practice of Ali, al-Zubayr, Sa'idah, and 'A'ishah. This allowance is reasoned by the Prophet's personal practice of praying two rak'ahs after Asr, which is interpreted by some as either making up a missed Sunnah (the two rak'ahs after Zuhr) or a specific concession for him, thereby not making it generally permissible for others to initiate non-causal voluntary prayers then.