What is the ruling of Islamic Law regarding one who slaughters a ewe and it turns out to have been pregnant, and is it permissible to slaughter the ewe if one knows it is pregnant?
Praise be to Allah, and peace and blessings upon our master, the Messenger of Allah.
If a person slaughters a ewe and it turns out to have been pregnant, the fetus becomes lawful (ḥalāl) by virtue of its mother's slaughter (tabaʿan li-ummihā).
It is stated in Mughnī al-Muḥtāj (Vol.6/P.158): "A fetus found dead [after the mother's slaughter], or found alive but in a state resembling that of a slaughtered animal [i.e., dying shortly after], becomes lawful — whether or not it had grown fur — provided it is found in the womb of a mother that was lawfully slaughtered, whether her slaughter was by cutting the throat, or by an arrow or hunting dog sent after her. This is based on the ḥadīth: 'The slaughtering of the fetus is [effected by] the slaughtering of its mother' [narrated by al-Tirmidhī, who graded it ḥasan, and by Ibn Ḥibbān, who graded it ṣaḥīḥ] — meaning that the slaughter which rendered the mother lawful renders the fetus lawful as well, by virtue of following her; and because the fetus is one of her constituent parts, and her slaughter renders lawful all of her parts."
This ruling differs, however, from the case of one who knows from the outset that the ewe is pregnant [and intends to sacrifice her specifically as the udḥiyah while pregnant] — in which case, according to the Shāfi'ī school, she does not fulfill the requirement of a valid sacrifice.
It is stated in Ḥāshiyat al-Bujayrimī 'alā al-Khaṭīb (Vol.4/P.335): "A pregnant animal does not fulfill the requirement [of a valid sacrifice], and this is the authoritative position (al-mu'tamad), because pregnancy diminishes the quality of the meat. As for why such an animal is nevertheless counted as complete [i.e., fully valid] in matters of zakāh, that is because the intent there is reproduction (nasl), not the quality of the meat.". And Allah, the Most High, knows best.
Does buying meat equivalent to the weight of a slaughtered animal and distributing it avail for an udhiyah?
Praise be to Allah, and prayers and peace be upon our Master the Messenger of Allah.
That does not avail for the sacrifice (uḍḥiyyah), because the sacrifice necessarily requires slaughtering an animal from the category of anʿām (camels, cattle, and sheep/goats) within a specified time.
Rather, that is considered a form of charity (ṣadaqah) for which one is rewarded, but not an udhiyah. And Allah Almighty knows best.
What is the ruling on sacrificing a castrated animal or one with a missing tail?
Praise be to Allah, and peace and blessings be upon our master, the Messenger of Allah.
It is permissible to sacrifice a castrated sheep; as it has been established that the Prophet (peace be upon him) sacrificed:
"...two large, fat, horned, white-and-black, castrated rams (Mawju'ayn—meaning having crushed testicles)." [Narrated by Ibn Majah in his Sunan].
It is not permissible to sacrifice an animal that is missing its tail, or udder due to being cut off. This is in contrast to an animal that was naturally born without a tail, or udder; such an animal is valid for sacrifice. And Allah the Almighty knows best.
Someone wiped over his shoes after wearing them in a state of purity, then took them off and prayed without them?
Ablution is not invalidated by taking off leather socks or shoes after wiping over them. However, whoever takes them off after wiping must wash his feet only. If he prayed without washing his feet, he must wash his feet and repeat the prayer. And Allah the Almighty knows best.