He wants to donate his udhiyah so that his wife and children can travel
Question

                I have a friend who lives in Germany; he is a university student and is married with one daughter. His wife and daughter are not going to spend Eid with him; rather they are going to travel to his country and he is going to stay in Germany by himself. He has offered a sacrifice every year since he got married, but this year he wants to donate his udhiyah to a family in need, because he is going to spend Eid in Germany on his own, and he can only afford one udhiyah. Should he donate it or should he offer the udhiyah himself? 

Please note that that he is a student and does not have a fixed income; rather he works when he is not studying. Is it permissible for him to donate it or not?.
Praise be to Allah.
    Offering the udhiyah is a confirmed Sunnah (Sunnah 
    mu’akkadah) that should be done regularly and it should be done openly and 
    propagated among the Muslims. Some of the scholars are of the view that it 
    is obligatory; hence to be on the safe side, it is better not to omit it 
    except if one has an excuse. 

    Slaughtering the udhiyah is preferable to giving its price in 
    charity or donating a sheep, because by slaughtering it one draws closer to 
    Allah, may He be exalted, and makes the ritual manifest. 

    Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) 
    said: 

    The udhiyah and ‘aqeeqah and hadiy are better than giving the 
    price thereof in charity; if a person has wealth that he wants to use to 
    draw close to Allah, he should offer the sacrifice himself.

    Majmoo‘ al-Fataawa, 26/304 

    It says in Kashshaaf al-Qinaa‘ (1/21): Slaughtering 
    the ‘aqeeqah is preferable to giving its price in charity. The same also 
    applies to the hadiy. This was stated clearly by Ibn al-Qayyim in Tuhfat 
    al-Mawlood and by Ibn Nasr in his Hawaashi, because the Prophet 
    (blessings and peace of Allah be upon him) and the caliphs offered 
    sacrifices; if giving charity was better, they would have done that. And 
    because of the hadeeth of ‘Aa’ishah, which is attributed to the Prophet 
    (blessings and peace of Allah be upon him): “The son of Adam does not do any 
    deed on the Day of Sacrifice that is more beloved to Allah than shedding 
    blood; it (the sacrifice) will come on the Day of Resurrection with its 
    horns and hooves and hair, and Allah appreciates the blood before it reaches 
    the ground, so do it gladly.”

    Narrated by Ibn Maajah. [Classed as da‘eef by al-Albaani in
    ad-Da‘eefah, 526]. And because preferring to give in charity rather 
    than offer the sacrifice leads to forsaking the Sunnah of the Messenger of 
    Allah (blessings and peace of Allah be upon him). End quote. 

    But if your friend is aware of the need of a particular 
    family, then he may give charity to them in particular and not to anyone 
    else, and he may give them some charity (other than the udhiyah) and give 
    them a larger share (of the sacrifice) and keep a smaller share for himself 
    if he is going to spend Eid on his own and does not need his share of the 
    udhiyah. 

    If the needy family is not in the place where he is living, 
    then he may delegate someone to offer the udhiyah on his behalf in a country 
    or region where there are many needy people. 

    Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) 
    said: 

    If we say concerning the hadiy and udhiyah that it is 
    mustahabb to eat one third and give one third in charity, that only applies 
    if there is no reason to increase the portion of one of the categories of 
    recipients. But if it so happens that there are a lot of poor people, then 
    we regard it as preferable to give more than one third in charity; the same 
    applies if the poor have received meat in abundance (in this case, their 
    share may be reduced); and the same applies to what one may keep. Wherever 
    the need is greatest, that may change the ratios given to the three 
    categories of recipients.

    Majmoo‘ al-Fataawa, 19/258 
See also 
    question no. 36645 
If it so happens that the 
    family that your friend is helping are in need of money and their need will 
    not be met by giving them the meat from the sacrifice, and he does not have 
    any other money, as you mentioned in your question, and he does not have 
    anyone with him to whom he can give the meat or he has relatives who need 
    this money, then he may give this money to them in charity in this case, and 
    not offer the udhiyah this year. 
Shaykh al-Islam Ibn 
    Taymiyah (may Allah have mercy on him) said: 
(Voluntary) Hajj performed 
    in the prescribed manner is better than charity that is not obligatory. But 
    if a person has relatives who are in need, then giving charity to them is 
    preferable. The same applies if there are people who are in need of his 
    spending. But if both actions are voluntary then Hajj is better, because it 
    is an act of worship that is both physical and financial. Similarly, 
    offering the udhiyah and ‘aqeeqah is preferable to giving their price in 
    charity. 
Al-Fataawa al-Kubra, 
    5/382; al-Ikhtiyaaraat, 116 
And Allah knows best.