Is washing the private part after urinating (Istinjaa`) a condition, and is it done with water and soap, or with water only?
Istinjaa` is obligatory for removing impurity, and it can be done with toilet paper, or a stone, or water. It is preferable to do Istinjaa` first with paper, or stone, or the like, then to wash the private part with water until making sure that the impurity has been removed. Using soap is not a condition, but there is no harm in doing so provided that it is washed off with water. It is also permissible to use either water, or paper if impurity is removed by any.
When is a child instructed to fast?
A child is instructed to fast at the age of seven if they are capable of fasting and have reached the age of discernment, by analogy to prayer. They should be encouraged but not forced, so they can become accustomed to it. It is obligatory for their guardian, whether a father or another, to instruct them.
What is the ruling on performing dry ablution (tayammum) on a wall or stone?
One of the conditions for tayammum is that it be with pure, clean dust (soil). It is not valid to perform tayammum by striking stones, a wall, sand that has no dust (i.e., that does not produce dust), pebbles alone, or clay, as these are not from the earth or its same category. And Allah the Almighty knows best.
A woman became pure [from menstruation] before Fajr, but did not perform ghusl until after sunrise — what is the ruling on her fast?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Her fast is valid, since ghusl (ritual bathing) is not a condition for the validity of the fast, but rather for the validity of the prayer. However, she is sinful for delaying the Fajr prayer beyond its designated time without a valid excuse.
It is known that the time for Fajr prayer ends at sunrise. Nevertheless, she must still perform ghusl, and make up the Fajr prayer. And Allah, the Exalted, knows best.