Slaughtering camels standing, untethered or with the left foreleg tethered

Allah, the Blessed and Exalted, says: "Then when they fall (lifeless) on their sides." [Surah al-Hajj: 36]
Imam Mujahid (may Allah have mercy on him) says: "(It means) when they fall to the ground."

Sayyiduna Anas (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) led the Zuhr prayer in Madinah with four rak'ahs while we were with him, and he (peace and blessings be upon him) led the Asr prayer at Dhul-Hulayfah with two rak'ahs. Then he spent the night there, and in the morning he mounted his riding camel. When it climbed onto al-Bayda', he (peace and blessings be upon him) said 'Allahu akbar' (Allah is the Greatest), 'Subhan Allah' (Glory be to Allah) and 'Al-hamdu lillah' (All praise is for Allah), then he entered ihram with the talbiyah for Hajj and Umrah, and then the people also entered ihram with the talbiyah for Hajj and Umrah. When we arrived (in Makkah), he (peace and blessings be upon him) commanded them: "Change it into Umrah," and then they entered ihram for Hajj on the 8th of Dhul-Hijjah. The Messenger of Allah (peace and blessings be upon him) slaughtered seven camels with his own hand while they were standing, and in Madinah he (peace and blessings be upon him) sacrificed two horned black-and-white rams.

Sayyiduna Abdullah bin Qurt (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "The best of days with Allah is the day of sacrifice, then the day of al-Qarr, on which the people stay settled," that is, the day that follows the day of sacrifice. Five or six sacrificial camels were brought forward to the Messenger of Allah (peace and blessings be upon him), and they began drawing close to him (as if to see) with which of them he would begin. When they fell on their sides, the Messenger of Allah (peace and blessings be upon him) said something softly that I did not understand. I said to the person at my side: What did he (peace and blessings be upon him) say? He said: He (peace and blessings be upon him) said: "Whoever wishes may cut off (a portion)."

Ziyad bin Jubayr (may Allah have mercy on him) says that Ibn Umar (may Allah be pleased with them both) passed by a man who was slaughtering his camel after making it kneel. He said: Make it stand, tied (and then slaughter it); this is the Sunnah of your Prophet (peace and blessings be upon him).

Sa'id bin Jubayr says: I saw Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) make his sacrificial camel stand and tie up one of its forelegs; it was standing on three legs while he slaughtered it.

Abu Zabyan says that Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) used to recite this word as: "So mention the name of Allah over them while they stand (sawafin)" [Surah al-Hajj: 36], and he would say: (It means) tied, standing on three legs. Then he would say: 'Bismillahi wallahu akbar, Allahumma minka wa laka' (In the name of Allah, and Allah is the Greatest; O Allah, it is from You and for You). The narrator says: He was asked about their hides, and he said: One may give them in charity or benefit from them oneself.

Mujahid (may Allah have mercy on him) says: Whoever recites it as "sawafin" says (it means): "It is tied," and whoever recites it as "sawaff", (it means): "Lined up in front." [Sahih. Recorded by al-Tabari in his Tafsir: 9/152]

Abd al-Rahman bin Sabit (may Allah have mercy on him) says that the Prophet (peace and blessings be upon him) and his Companions (may Allah be pleased with them) used to slaughter camels with the left (foreleg) tied, standing on their remaining legs.
The hadith of Ibn Jurayj from Abu al-Zubayr from Jabir is mawsul (connected), and his hadith from Abd al-Rahman bin Sabit is mursal.