Is it permissible to eat chicken and eggs together, or milk and beef? I hear this is not permissible. I'd appreciate answers with evidence and not just opinions.
Prohibited to you are dead animals, blood, the flesh of swine, and that which has been dedicated to other than Allah , and [those animals] killed by strangling or by a violent blow or by a head-long fall or by the goring of horns, and those from which a wild animal has eaten, except what you [are able to] slaughter [before its death], and those which are sacrificed on stone altars, and [prohibited is] that you seek decision through divining arrows. That is grave disobedience. This day those who disbelieve have despaired of [defeating] your religion; so fear them not, but fear Me. This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion. But whoever is forced by severe hunger with no inclination to sin - then indeed, Allah is Forgiving and Merciful.
--- Al-Ma'idah 3 ---
About mixing chicken and eggs, or beef and milk, I have never heard of any such prohibition in Islam: The meat-and-milk issue, at least, is prohibited in Judaic dietary law (Wiki: Kashrut), but that is not binding on Muslims at all. Perhaps the people you hear this from are confusing the two?
In Hanafi fiqh, the principle in all matters is that it is permissible unless stated otherwise; a rule we commonly follow as, "Innocent until proven guilty". This is the case in relation to all judicial matters and matters pertaining to Allah's worship, which means that all forms of worship of Allah, in a way that outrightly seems permissible to the naked eye of somebody else, is allowed. Eg. You cannot place a photo in front of you and prostrate towards it, claiming that you are worshipping Allah, as somebody else may assume you to be worshipping and bowing before the photo, not Allah.
As for the previous-mentioned case, location must be taken into consideration. Eg. If you are in a Muslim majority country, or a country governed by Muslims, you can be sure that all meat is primarily halal, unless specified. As for the UK, the regulation of meat is that it be stunned, not slaughtered. As a result, we must look for a 'suitable for vegetarian' or 'Halal' certified logo (either HMC or HFA) to show it is suitable for our consumption. Based on the case mentioned in the previous post, it would mean that all foods, including Haribos and all foods that are made/fried in the same oil as those as haram foods, should be considered lawful for consumption.
It should be understood that not everything is a clear as black and white; not everything is simply Fardh or Haraam. There are many things to suggest that we should not eat for our own welfare, however, that does necessarily render that food to be haraam. I would advise seeking a professional answer from a qualified scholar (not from somebody whom Google qualifies for instance), one with strong evidence so that you may be satisfied.
And Allah and His Messenger SalAllahu 'Alaihi Wasallama know best.