What is the ruling on performing voluntary (nafl) prayer during the time of istiwā' (the sun's zenith) on the day of Jumu‘ah (Friday), and is this ruling specific to someone who has come to the mosque to perform the Jumu‘ah prayer?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
It is permissible to perform voluntary (nafl) prayer during the time of istiwā' (the sun's zenith, i.e., its highest point before noon) on the day of Jumu‘ah (Friday) — whether for someone who is attending the Friday prayer or someone who is not, and whether they are among the people obligated to attend it or not.
It is stated in Mughnī al-Muḥtāj (Vol.1/P.310): "The more correct position (al-aṣaḥḥ) is that prayer is permissible during this time without restriction — regardless of whether the person will be attending the Jumu‘ah prayer or not." And Allah, the Exalted, knows best.
What is the Du`a (supplication) of Istikhara (guidance prayer)?
O Allah, I consult You as You are All-Knowing and I appeal to You to give me power as You are Omnipotent, I ask You for Your great favor, for You have power and I do not, and You know all of the hidden matters. O Allah! If you know that this matter (then he should mention it) is good for me in my religion, my livelihood, and for my life in the Hereafter, or he said: "for my present and future life" then make it (easy) for me. And if you know that this matter is not good for me in my religion, my livelihood and my life in the Hereafter, or he said: "for my present and future life" then keep it away from me and take me away from it and choose what is good for me wherever it is and please me with it."
What is the ruling of Islamic Law on following the actions of the imam in prayer and how this following is achieved?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
The follower (ma'mum) is required to follow his imam in the actions of the prayer. This "following" (mutaba'ah) means that the follower performs each action of the prayer after the imam has begun it but before he has finished it. For example, the follower bows (in ruku') after the imam has reached the position of bowing, then rises after the imam has risen. The Prophet, peace and blessings be upon him, said: "The imam is only appointed to be followed, so when he says the takbir, say the takbir; and when he bows, then bow; and when he prostrates, then prostrate" (agreed upon, i.e., reported by both al-Bukhari and Muslim).
It is stated in Mughni al-Muhtaj (1/505): "Among the conditions of valid congregational prayer (iqtida') is following the imam in the actions of the prayer... meaning that following the imam is obligatory in the physical actions of the prayer, not in its verbal utterances... Complete following (kamal al-mutaba'ah) is achieved when the follower's beginning of an action comes after the imam's beginning of that same action, while the follower's beginning of the action precedes the imam's completion of it" — end of quote, with slight paraphrasing.
And Allah, the Exalted, knows best.
Is a person who is in a state of Janabah (major ritual impurity due to having a marital intercourse, ejaculation, menstruation, and post-delivery impurities) sinful if he/she goes about his/her daily life activities in that state i.e. without making Ghusl (ritual bath)?
It goes without saying that a Muslim should always be in a state of ritual purity so as to be able to perform prayers and recite Quran. It is from Sunnah (Prophetic tradition) that a Muslim hastens to make Ghusl from Janabah, but he/she is not sinful in case he/she delayed that provided that he/she doesn`t miss prayers. However, it is permissible for him/her to go about their daily activities while in a state of Janabah, but had better bathe in order not to miss any prayer.