Is it permissible for a woman to lead other women in prayer?
Yes, it is permissible for a woman to lead other women in prayer. The most knowledgeable among them in the rulings of prayer should act as the imam. She should stand in the middle of the row, slightly ahead of the others.
What is the ruling on performing the standing (qiyām) and bowing (rukū‘) portions of the prayer normally, while performing the prostration (sujūd) seated due to knee pain?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
If performing sujūd (prostration) in prayer causes the worshipper pain in the knees, then it is permissible for him to perform it through gesture (īmā') while seated, since Allah, Glorified and Exalted is He, has lifted hardship from His servants. On the authority of ‘Imrān ibn Ḥuṣayn (raḍiyallāhu ‘anh), he said: "I suffered from hemorrhoids, so I asked the Prophet ﷺ about [how to perform] the prayer, and he said: 'Pray standing; if you are unable, then sitting; and if you are unable, then on your side.'" [Ṣaḥīḥ al-Bukhārī]
If the valid excuse later subsides, the worshipper is then obligated to perform the prayer with all its pillars and conditions fully observed — including standing, rukū‘ (bowing), and sujūd (prostration). And Allah, the Exalted, knows best.
Is it permissible for a pious Muslim woman to stay with her husband who had quit praying out of laziness?
Quitting prayer is one of the major grave sins that come after disbelieving in Allah, but the wife of such a person isn`t considered divorced, rather, she should exert all her efforts in order to bring him back to the way of Islam. However, if his sin is likely to lure her from the way of Islam, then she had better separate from him by lawful means such as Mokhal`aa (When a wife pays a compensation for her husband in return for divorcing her). Moreover, if she exercises patience, and remains steadfast on her faith, then there is no harm in doing that.
What is the validity of the formula for sending blessings upon our master Muḥammad ﷺ: *"Allāhumma ṣalli wa sallim wa bārik ‘alā sayyidinā Muḥammad wa ‘alā ālihi, ‘adada kamāli-Llāhi wa kamā yalīqu bikamālihi"* ("O Allah, send blessings, peace, and grace upon our master Muḥammad and his family, by the number of Allah's perfection, and as befits His perfection")?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
It is permissible to send blessings upon our master, the Prophet ﷺ, using the formula mentioned in the question, since sending blessings upon the Prophet ﷺ is an act of devotion legislated in its basic essence, without a specific prescribed wording required outside of the formal prayer itself. It is therefore valid to perform it outside of prayer using any formula. This particular formula involves multiplying the blessings sent upon the Chosen Prophet ﷺ to the number of the perfections of Allah, the Exalted — which are limitless — so that, by Allah's permission, its reward and benefit never cease.
The meaning of "the number of Allah's perfection" is that it is without limit, making the blessings sent boundless, corresponding to His perfection, Glorified is He, which cannot be enumerated or counted. This formula is analogous to the words of our Greatest Prophet ﷺ, as related in the authentic ḥadīth narrated by Imam Muslim: the Prophet ﷺ said to Sayyidah Juwayriyyah (raḍiyallāhu ‘anhā): "Indeed, I said four phrases after you [left], three times, which, if weighed against everything you have said since this morning, would outweigh them: Subḥān Allāhi wa biḥamdihi, ‘adada khalqihi, wa riḍā nafsihi, wa zinata ‘arshihi, wa midāda kalimātihi" (Glory be to Allah, and praise be to Him, by the number of His creation, by His pleasure, by the weight of His Throne, and by the extent of His words). And Allah, the Exalted, knows best.