Matthew 5:36

You should not take an oath, [saying] 'by my head,' for you cannot make a single hair white or black.

Matthew 6:27

And which one of you can worry yourself into living a single day longer?

Matthew 23:16-21

"It is too bad for you blind leaders who say that whoever takes an oath 'by the Temple,' it does not [really] mean anything, but whoever takes an oath 'by the gold of the Temple,' he is obligated to [fulfill] the oath.

Luke 12:25

And which one of you can worry yourself into living a single day longer?

Treasury of Scripture Knowledge

Summary

Neither shalt thou swear by thy head, because thou canst not make one hair white or black.

General references

Bible References

Shalt

Matthew 23:16
"It is too bad for you blind leaders who say that whoever takes an oath 'by the Temple,' it does not [really] mean anything, but whoever takes an oath 'by the gold of the Temple,' he is obligated to [fulfill] the oath.

Because

Matthew 6:27
And which one of you can worry yourself into living a single day longer?
Luke 12:25
And which one of you can worry yourself into living a single day longer?

General references

Luke 12:25
And which one of you can worry yourself into living a single day longer?