Is Kissing on the Lips Among Women Prohibited?
Question

I have an important question which I hope you will answer. Please excuse us for this question, but we need to explain it to you so that we may avoid something haram. 

It has become very common among girls who claim Islamic sisterhood to kiss one another in an exaggerated fashion, such as kissing on the mouth or elsewhere, and they claim that this is part of complete love.
When we explain to them that it is prohibited, they say that there is no Shar`i evidence to show that it is prohibited, and that the Messenger (peace and blessings of Allah be upon him) used to bite the tongue of Zayd ibn Harithah, and that they are prepared to stop doing this if they are shown any Shar`i evidence that it is haram.
Praise be to Allah.What leads to falling into something forbidden is also forbidden
In order to establish a Shar`i ruling, it is not essential that there be a text which speaks specifically of it in a Quranic verse or a Hadith of the Prophet (peace and blessings of Allah be upon him). There is no end to issues and new matters. Hence Islam has set out basic principles which cover thousands of issues and explain their rulings. These major principles include the principle of Sadd Adh-Dhara`i (blocking the means).
In I`lam Al-Muwaqqi`in, Ibn Al-Qayyim (may Allah have mercy on him) mentioned ninety-nine texts from the Quran and Sunnah which point to the soundness of this principle. What is meant by “blocking the means” is that everything that is a means that leads to falling into something  forbidden is also forbidden, even if it is permissible in principal. 
Islam closes the door to things that lead to immorality
It is well known that Islam closes the door to things that lead to immorality, whether it is Zina or perversions thereof such as homosexuality or lesbianism . Among the ways in which it has closed the door to that are the following: 

Forbidding men to look at women and vice versa, forbidding a man to be alone with a non-Mahram woman or to shake hands with her, forbidding a woman to travel alone, and so on. Another example is the way in which Islam closes the door to perversion and immorality that may occur between males or between women, so Islam forbids a woman to look at the `Awrah of another woman , or a man to look at the `Awrah of another man ; it forbids sleeping in one bed beneath one cover; and it forbids looking, touching and kissing if that is done with desire, even between one woman and another, or between one man and another. 

It was narrated from Abu Sa`id Al-Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: “No man should look at the `Awrah of another man, and no woman should look at the `Awrah of another woman. No man should lie down with another man beneath a single cover, and no woman should lie down with another woman beneath a single cover.” (Narrated by Muslim, 338) 
Is kissing on the lips prohibited? 
The scholars have also clearly stated that this applies even between Mahrams (close blood relatives). They have stated that it is forbidden for a father to kiss his daughter on the mouth and that it is even more forbidden for a brother to kiss his sister on the mouth, let alone other relatives. 
Imam Ahmad (may Allah have mercy on him) was asked about a man kissing a woman who is his Mahram. He said: If he has come from a journey and he does not fear that there may be any temptation. Ibn Muflih (may Allah have mercy on him) said: But he should never do that on the mouth; it should be on the cheek or on the head. (Al-Adab Ash-Shar`iyyah, 2/256) 
Imam Ahmad (may Allah have mercy on him) has mentioned the following limitations with regard to kissing Mahrams: 

There should be a special reason for it, such as having come from a journey.
There should be no risk of Fitnah (temptation). 

Ibn Muflih (may Allah have mercy on him) has explained an important point which is that there should be no kissing on the mouth, rather it should be on the cheek or head, because kissing the mouth has to do with desire, not the kissing of emotion such as that of a father or brother. This is clear to anyone who thinks about it. 
In Al-Iqna` (3/156) it says: 
“There is nothing wrong with one who has come from a journey kissing his female Mahrams, so long as he does not fear that there may be any temptation, but he should not kiss on the mouth, rather it should be on the forehead or head.” 
In Al-Mawsu`ah Al-Fiqhiyyah (13/130) it says: 
“It is not permissible for a man to kiss the mouth or hand or anything else of another man, or for a woman to kiss another woman, or to embrace or touch their bodies, etc., if that is done by way of desire. There is no difference of opinion among the jurists` on this matter … 
But if that is not done on the mouth, and it is done by way of respect and honouring, or to express emotion upon meeting and parting, then there is nothing wrong with it.” 
If these are the words of our scholars and imams with regard to kissing Mahrams such as a daughter, then how can they allow non-Mahram females to kiss one another on the mouth on a daily basis, with no reason such as travelling or a lengthy absence? 
In the answer to question no. 60351 , you will find important details on the ruling on schoolgirls kissing one another on a daily basis. What is said there about it not being allowed applies even more so to kissing on the mouth. 
It should be noted that we cannot find the Hadith mentioned in the question about the Prophet (peace and blessings of Allah be upon him) biting the tongue of Zayd ibn Harithah, and we do not know where this comes from. 
In At-Tirmidhi (2732) it is narrated that `Aishah (may Allah be pleased with her) said: Zayd ibn Harithah came to Madinah and the Messenger of Allah (peace and blessings of Allah be upon him) was in my house. He came to him and knocked at the door, and the Messenger of Allah (peace and blessings of Allah be upon him) stood up and embraced him and kissed him. 
But this is a inauthentic Hadith, which was classed as such by Al-Albani in Da`if At-Tirmidhi. 
And Allah knows best.