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 tasting food while fasting?
Tasting food while fasting is disliked (makruh). However, if any part of the food reaches the body cavity (jauf), the fast becomes invalid.
I read the Qudsī ḥadīth: "Whoever breaks his wuḍūʾ and does not perform ablution has shown me harshness; whoever performs ablution and does not pray has shown me harshness; whoever prays and does not supplicate to Me has shown me harshness; and whoever supplicates to Me and I do not answer him, then I have been harsh to him, and I am not a harsh Lord." What is the authenticity of this ḥadīth?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
This ḥadīth was mentioned by al-Ṣaghānī (may Allah have mercy on him) in al-Mawḍūʿāt (p. 43), where he said: “Among them is their saying: ‘Whoever breaks his wuḍūʾ and does not perform ablution has shown me harshness; whoever performs ablution and does not pray has shown me harshness; (whoever prays and does not supplicate to Me has shown me harshness); and whoever supplicates to Me and I do not answer him, then I have been harsh to him, and I am not a harsh Lord.’”
Al-ʿAjlūnī (may Allah have mercy on him) cited what al-Ṣaghānī said in Kashf al-Khafāʾ (Vol.2/p.264). And Allah Almighty knows best.
How is night prayer offered?
Night prayer is offering voluntary prayer after Maghrib and before Fajr (Dawn). As for Tahajjud, it is offering voluntary prayer at night after waking up voluntarily, and for Allah`s sake as He Says (What means): "And pray in the small watches of the morning: (it would be) an additional prayer (or spiritual profit) for thee: soon will thy Lord raise thee to a Station of Praise and Glory!" [Al-Isra`/79]. Offering Tahajjud is better than offering voluntary prayer before going to bed.