Praise be to Allah.
Lying is prohibited
If he takes leave based on his saying that he is going for ‘Umrah, and in fact he does not intend to go, then this is lying . If that results in him getting leave to which he is not entitled, then the salary that he gets for this period is haram wealth and is not permissible for him.
The one who does that has to repent to Allah and go back to work.
Does lying break your fast?
With regard to the effect of lying on fasting and prayer, they are valid, but it indicates that he is not doing them as Allah enjoined. If he was really praying as Allah has enjoined, then his prayer would be preventing him from doing evil deeds, as Allah says (interpretation of the meaning):
“Verily, As-Salah (the prayer) prevents from Al-Fahsha (i.e. great sins of every kind, unlawful sexual intercourse) and Al-Munkar (i.e. disbelief, polytheism, and every kind of evil wicked deed).” [al-'Ankabut 29:45]
Effect of sins on fasting
Undoubtedly sins such as lying, deceiving , swearing , insulting others etc., detract from the reward of the one who is fasting, because the Prophet (peace and blessings of Allah be upon him) said: “Whoever does not give up false speech and acting upon it and ignorant conduct, Allah has no need of his giving up his food and drink.” (Narrated by al-Bukhari, 6057)
It was narrated by al-Tabarani in al-Mu’jam al-Saghir and al-Mu’jam al-Awsat with the wording: “Whoever does not give up obscene talk and lying, Allah has no need of his giving up his food and drink.” (Classed as hasan by al-Albani in Sahih al-Targhib wa’l-Tarhib)
False speech has also been interpreted as referring to lying. This points to the abhorrence of lying when fasting, and shows that he is exposing his fast to rejection and lack of acceptance.
It says in al-‘Awn al-Ma'bud:
“If he does not give up” means, if he does not refrain from. “False speech” means lying. “Allah has no need” – Ibn Battal said: This does not mean that he is enjoined to stop fasting, rather what it means is a warning against false speech and the other things mentioned. … Ibn al-Munir said: Rather it is an indication that it will not be accepted. Ibn al-‘Arabi said: What this hadith means is that he will not be rewarded for his fasting … This hadith was quoted as evidence to show that these actions detract from the reward of fasting.”
And Allah knows best.