Is it permissible to say "Thank you, my Lord?"

The phrase is legitimate and permissible, because Allah is the One deserving of thanks, and thanks (shukr) is synonymous with praise (hamd). Sacred texts have indicated the command to thank Allah, such as His saying, "Give thanks to Allah" and "Be among the thankful." However, it is advisable to avoid this phrase if some people think its meaning resembles the thanking of servants to one another, or if it is used in a trivial way that does not befit Allah's majesty. So, let the servant use what is beyond doubt.