What is the ruling on deliberate lying in Ramadan daytime?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

Fasting is a secret act of worship between a slave and his Lord Who is The Only One to have full knowledge about it. This is so since it comprises two hidden actions: an innermost intention, which is known only to Allah, and abstention from desires that man usually fulfills in secret. The ultimate purpose for which fasting is prescribed is to attain piety. Allah Almighty Says (what means): {O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become pious.}[Quran 2: 183] 

Please note that drawing close to Allah is not attained by abstention from permissible desires outside fasting.  Rather, the person first has to seek closeness to Allah by renouncing what He has declared unlawful such as lying, injustice and so on, and he has to do so in all his cases.  In this regard, the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever does not give up false speech and acting accordingly, Allah does not need him to give up his food and drink.” [Al-Bukhari] 

In another narration, the Prophet, sallallaahu ‘alayhi wa sallam, said: “Fasting is not to abstain from food and drink; rather it is to abstain from idle talk and obscene language.”

Moreover, Jaabir ibn ‘Abdullaah said:

The day you fast, you must preserve your hearing, sight, and tongue form lying and other forbidden acts. Also, you must refrain from bothering your neighbors. The day you fast, you should show tranquility and self-respect. You should make the day you fast different from your other ordinary days.

 Whoever lies while fasting must turn to Allah in repentance, ask Him for forgiveness, and be determined not to lie again. However, one is not required to make up for the day of fasting in which one told lies.