All praises due to Allah and may His peace and blessings be upon the Last and Final Messenger Muhammad.
In Sahih Muslim, Book of Menstruation, chapter on Tayammum:
Abd al-Rabmin b. Abza narrated It on the authority of his father that a man came to ‘Umar and said: I am (at times) affected by seminal emission but find no water. He (‘Umar) told him not to say prayer. ‘Ammar then said. Do you remember,0 Commander of the Faithful, when I and you were in a military detachment and we had had a seminal emission and did not find water (for taking bath) and you did not say prayer, but as for myself I rolled in dust and said prayer, and (when it was mentioned before) the Apostle (may peace be upon him) said: It was enough for you to strike the ground with your hands and then blow (the dust) and then wipe your face and palms. Umar said: ‘Ammar, fear Allah. He said: If you so like, I would not narrate it.
A hadith like this has been transmitted with the same chain of transmitters but for the words: ‘Umar said: We hold you responsible for what you claim.”
Based on above narration some people allege that Umar bin Khattab (ra) was unaware of the verses of Tayammum. Basically Tayammum has been mentioned at two places in the Qur’an. First in Surah Nisa verse 43:
“O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying or in a state of janabah, except those passing through [a place of prayer], until you have washed [your whole body]. And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and find no water, then seek clean earth and wipe over your faces and your hands [with it]. Indeed, Allah is ever Pardoning and Forgiving.” [Qur’an 4:43 tr. Sahih International]
And in Surah Ma’idah verse 6:
“O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. And if you are in a state of janabah, then purify yourselves. But if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and wipe over your faces and hands with it. Allah does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful.” [5:6]
Sayyiduna ‘Umar (ra) was certainly aware of this verse and he also held it permissible to perform Tayammum in case of minor impurity [i.e. when only ablution is necessary] when there is no water available. But according to him it was not permissible to perform Tayammum in case of major impurity [i.e. when Ghusl is necessary]. In the above two verses if the word “lams” is taken for sexual intercourse then it does go against ‘Umar (ra), however if it is taken to mean physical touch then it is not a proof against his opinion. Basically the meaning of that part is controversial among scholars. According to Imam Shafi’i the part “Lamastumun Nisa” means touching of women while according to Imam Abu Hanifa it means sexual intercourse. So Umar (ra) was not actually unaware of the verses of Tayammum but he considered them to be only for those who with minor impurity but not in case of Janabah. It was a matter of Ijtihad not like some Rawafidh are trying to portray as though he was simply ignorant of the verses of Qur’an. It is said that he left this opinion. And Allah knows best.
Another point which clearly shows that the verse is not decisive against the view held by ‘Umar (ra) is the fact that in the incident which happened between him and ‘Ammar bin Yasir (ra) regarding the issue Ammar (ra) reminded him of an incident happened during the lifetime of the Prophet (sallallahu ‘alaihi wa sallam) and not the verses regarding Tayammum. There could not have been any evidence stronger than the verse of Qur’an and ‘Ammar (ra) would never had left it if it were against ‘Umar (ra).