זה הדבר אשר צוה השם לאמר… (ויקהל לה:ד)

Rashi says: “לי לאמר לכם” – Hashem told me that I should tell you.

Chazal say that Moshe Rabbeinu was very distraught and did not bring anything for the work of the Mishkan.  So Hashem told him: Your “telling” the Yidden to get donations is considered a donation towards the Mishkan. This is what the passuk alludes to “זה הדבר אשר צוה השם לאמר”says Rashi, “לי” – Hashem commanded I should give my donation towards the Mishkan by “לאמר” by telling you “לכם” – you should bring donations for the Mishkan.