Me and brother co-own a plot of land. My question is, is it permissible for me to wakaf my portion of the land? Hope for an explanation.
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Wakaf or property endowment is among the encouraged deeds in Islam. This is due to the fact that its rewards are continuous for those who do so with sincerity for Allah SWT. This is based on the statement of Allah SWT:
لَن تَنَالُوا الْبِرَّ حَتَّىٰ تُنفِقُوا مِمَّا تُحِبُّونَ ۚ وَمَا تُنفِقُوا مِن شَيْءٍ فَإِنَّ اللَّـهَ بِهِ عَلِيمٌ
“Never will you attain the good [reward] until you spend [in the way of Allah] from that which you love. And whatever you spend – indeed, Allah is Knowing of it.”
Surah Ali Imran (92)
There is an interesting story related to the reaction of the companions when the verse is revealed. In a hadith from Anas bin Malik where he said, Ishaq ibn Abdullah ibn Abi Talha heard Anas ibn Malik say, “Abu Talha had the greatest amount of property in palm-trees among the Ansar in Madina. The dearest of his properties to him was Bayruha which was in front of the mosque. The Messenger of Allah, may Allah bless him and grant him peace, used to go into it and drink from the pleasant water which was in it.”
Anas continued, “When this ayat was sent down ‘You will not obtain rightness of action until you expend of what you love,’ (Sura 2 ayat l76), Abu Talha went to the Messenger of Allah, may Allah bless him and grant him peace, and said, ‘Messenger of Allah! Allah, the Blessed, the Exalted, has said, “You will not obtain until you expend of what you love.” The property which I love the best is Bayruha. It is sadaqa for Allah. I hope for its good and for it to be stored up with Allah. Place it wherever you wish, Messenger of Allah. ‘ “
“The Messenger of Allah, may Allah bless him and grant him peace, said,
بَخٍ، ذَلِكَ مَالٌ رَابِحٌ، ذَلِكَ مَالٌ رَابِحٌ، وَقَدْ سَمِعْتُ مَا قُلْتَ، وَإِنِّي أَرَى أَنْ تَجْعَلَهَا فِي الأَقْرَبِينَ
‘Well done! That is property which profits! That is property which profits. I have heard what you have said about it and I think that you should give it to your relatives.’ 
Then, Abu Talha said, ‘I will do it, Messenger of Allah!’ Abu Talha, therefore, divided it among his relatives and the children of his paternal uncle.” The narrators stated: “Among them are Ubay and Hassan.”
The same is stated in a hadith narrated by Abu Hurairah RA, the Prophet PBUH said:
إِذَا مَاتَ الإِنْسَانُ انْقَطَعَ عَمَلُهُ إِلاَّ مِنْ ثَلاَثَةٍ مِنْ صَدَقَةٍ جَارِيَةٍ وَعِلْمٍ يُنْتَفَعُ بِهِ وَوَلَدٍ صَالِحٍ يَدْعُو لَهُ
“When a man dies all his good deeds come to an end except three: Ongoing charity (Sadaqah Jariyah), beneficial knowledge and a righteous son who prays for him.” 
The wakaf itself means withholding a property that doesn’t depreciate in value and can be utilized or benefitted from by handing over its ownership to a user who exists and is permissible. 
In answering the above issue, musya’ or jointly owned property is permissible by syarak to be endowed even if it is just a portion of the property. This includes moveable assets such as a car or immovable assets such as a garden, land and others.  This is based on a hadith narrated from Abdullah bin Umar R.Anhuma, Umar RA said to the Prophet PBUH:
إِنَّ الْمِائَةَ سَهْمٍ الَّتِي لِي بِخَيْبَرَ لَمْ أُصِبْ مَالاً قَطُّ أَعْجَبَ إِلَىَّ مِنْهَا قَدْ أَرَدْتُ أَنْ أَتَصَدَّقَ بِهَا . فَقَالَ النَّبِيُّ صلى الله عليه وسلم”احْبِسْ أَصْلَهَا وَسَبِّلْ ثَمَرَتَهَا“
“The one hundred shares that I acquired in Khaibar -I have never acquired any wealth that I like more than that, and I want to give it in charity.’ The Prophet said: Freeze it and donate its fruits.” 
According to the above hadith’s text, it is permissible for us to endow the property we jointly own with another as long as the property is included as property that is permissible to be endowed and of value according to syarak. The reason is, only property that doesn’t depreciate interns of its physical value and is of benefit is permissible to be endowed according to syarak.
In this issue, in our opinion, it is permissible for an owner of a jointly owned property such as a garden of fruits to endow (wakaf) some or a part of his property. This is due to the fact that the deed’s sole purpose is to get closer to Allah SWT and not to gain any worldly rewards. Thus, this act is valid and accepted by Allah SWT.
Hopefully, this explanation benefits us all in understanding this religion of Islam better. Amin.