The Cow - 2:224
Do not make Allah an instrument of your oaths in order to appear good, virtuous and honest among the people. Allah Hears, Knows.
Related:
The Repentance/9:75
"Some of them even promised Allah, "If He grants us out of His bounty, we will spend our money for charity and we will be of the righteous people."
The Repentance/9:76
But when He gave them out of His bounty, they became stingy and turned away.
The Women/4:62
"If some calamity befalls them as a result of what they have done, they come to you and swear by Allah, "We only intended to do good and to reconcile"."
The Women/4:63
Allah knows what is in their hearts. Pay no attention to them, enlighten them, and speak to them kind words that will affect their character.
The Repentance/9:42
"If it had been a near benefit and a journey of moderate length, they would have followed you, but the way seemed far to them. They will swear by Allah: "Had we been able, we would have gone out with you."Thus they ruin themselves. Allah knows that they are liars."
The Repentance/9:62
They swear by Allah to please you. If they really believe, they should know that Allah and His messenger are more worthy to be pleased.