Am I obligated to offer expiation for an oath (kaffarat yameen) after saying to my friend in Syria, "By Allah, we pray for you every day," even though I do not pray for them daily?

If the one swearing by "Wallahi" (by God) does not intend an oath, then what occurred from him is considered a "laghw al-yamin" (idle oath) for which there is no expiation, in accordance with the Almighty's saying: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what your hearts have earned." As for lying to his friend that he prays for him every day, while not doing so, this is considered a forbidden lie from which one must repent. And if he intended the oath while knowing his statement was untrue, then that is a "yamin ghamus" (perjured oath).