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.
"I told my family at night: 'I will fast tomorrow as qaḍā' (a make-up fast),' but I forgot to make the intention before sleeping. Is my fast valid?"
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
The intention is obligatory in acts of worship. For obligatory fasting, the required intention is to resolve to fast during the night [before dawn]. Its proper locus is the heart, while verbalizing the intention out loud in acts of worship is a sunnah — so that the tongue may align with the heart. If the intent behind the statement in question was the intention to fast, then it is valid; but if the intent was merely to inform someone, or reflected hesitation or doubt, then it is not valid.
It is stated in *Bushrā al-Karīm* (Vol.1/P.216): "It is a sunnah to verbalize the intention — that is, whatever has already been intended in the heart, whether an obligatory or a voluntary act — such as specifying the number of rak‘ahs, just before the opening takbīr — so that the tongue may assist the heart, and because this is further removed from whispered doubts (waswasah), and in order to accommodate the view of those who held it obligatory in every act of worship that requires an intention (even though this is a minority position), by analogy with Ḥajj."
Accordingly: if the intention to fast arose in your heart before the second adhān [i.e., before Fajr], then your fast is valid.
And Allah, the Exalted, knows best.
Is bleeding that lasts for nine or ten days considered menstruation (Hayd)?
Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
If the duration of the bleeding does not exceed fifteen days, then all of it is considered menstruation (Hayd), even if the regular cycle ('Adah) has changed. And Allah the Exalted knows best.
What should the one performing the slaughter say at the time of slaughtering the 'aqīqah?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
It is Sunnah to say the following supplication at the time of slaughtering the 'aqīqah:
"Bismillāhi wallāhu Akbar, Allāhumma laka wa ilayka, hādhihi 'aqīqatu fulān."
("In the name of Allah, and Allah is the Greatest. O Allah, this is for You and unto You — this is the 'aqīqah of [the child's name].")
This is based on what al-Bayhaqī narrated in Al-Sunan al-Kubrā (Vol.9/P.511), that the Prophet ﷺ said: "Slaughter it in his name and say: In the name of Allah, and Allah is the Greatest. O Allah, this is for You and unto You — this is the 'aqīqah of so-and-so."
And Allah Almighty knows best.