Jeremiah 7:22-23
22 For I spake not unto your fathers, nor commanded them in the day that I brought them out of the land of Egypt, concerning burnt offerings or sacrifices:
23 But this thing commanded I them, saying, Obey my voice, and I will be your God, and ye shall be my people: and walk ye in all the ways that I have commanded you, that it may be well unto you.
Exodus 29:38-42
38 Now this is that which thou shalt offer upon the altar; two lambs of the first year day by day continually.
39 The one lamb thou shalt offer in the morning; and the other lamb thou shalt offer at even:
40 And with the one lamb a tenth deal of flour mingled with the fourth part of an hin of beaten oil; and the fourth part of an hin of wine for a drink offering.
41 And the other lamb thou shalt offer at even, and shalt do thereto according to the meat offering of the morning, and according to the drink offering thereof, for a sweet savour, an offering made by fire unto the Lord.
42 This shall be a continual burnt offering throughout your generations at the door of the tabernacle of the congregation before the Lord: where I will meet you, to speak there unto thee.
This passage in Jeremiah, which says that God did not command the Israelites concerning burnt offerings when they were brought out of the land of Egypt, is often paired with this passage from Exodus, alleging a contradiction.
What period of time is the passage in Jeremiah referring to? It's a time after the Lord called the Israelites His people, after He brought them out of Egypt, after He gave them commandments, and before He gave them burnt sacrifices.
Going back toward the beginning of Exodus, we can see where God promised to call them His people, before they had left Egypt:
Exodus 6:6-7
6 Wherefore say unto the children of Israel, I am the Lord, and I will bring you out from under the burdens of the Egyptians, and I will rid you out of their bondage, and I will redeem you with a stretched out arm, and with great judgments:
7 And I will take you to me for a people, and I will be to you a God: and ye shall know that I am the Lord your God, which bringeth you out from under the burdens of the Egyptians.
Later, when they had just left Egypt, and crossed the Red Sea, the Lord tells them that if they obey His commandments, He won't plague them with the plagues of Egypt:
Exodus 15:26
26 And said, If thou wilt diligently hearken to the voice of the Lord thy God, and wilt do that which is right in his sight, and wilt give ear to his commandments, and keep all his statutes, I will put none of these diseases upon thee, which I have brought upon the Egyptians: for I am the Lord that healeth thee.
Then, in Exodus 18:12, we see Moses's father-in-law Jethro offer a burnt offering before he returns to his land, but he was a priest of Midian (Exodus 18:1), and the Lord hadn't yet commanded the children of Israel anything concerning burnt offerings through Moses.
A little while later, God reiterates what He said about the Israelites becoming His people, if they obey Him:
Exodus 19:5-6
5 Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine:
6 And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel.
The people then agree to obey the Lord (Exodus 19:7-8), and Moses goes up to Mount Sinai.
God then gives Moses the Ten Commandments (Exodus 20:1-17), and afterward, a general rule about where burnt sacrifices are to be offered, without actually describing them (Exodus 20:24-26), and then a host of other judgments (Exodus chapters 21-23). He then comes down from the mountain, and reads the covenant to them, which they agree to obey:
Exodus 24:7-8
7 And he took the book of the covenant, and read in the audience of the people: and they said, All that the Lord hath said will we do, and be obedient.
8 And Moses took the blood, and sprinkled it on the people, and said, Behold the blood of the covenant, which the Lord hath made with you concerning all these words.
It's only after Moses goes back up to the mountain, some time during the 40 days he is up there (Exodus 24:18), that he begins to receive the instructions about the actual burnt offerings and sacrifices, as pointed out above in Exodus 29:38-42.
So, what we see are all the elements described in Jeremiah 7:22-23 - God calling the Israelites His people, issuing commandments, and promising them blessings if they obey - in plenty of passages before God ever issued commands regarding burnt sacrifices. The only question is what the exact time cutoff is, which will depend on how we view Exodus 20:24.
If we are counting Exodus 20:24 as the first command concerning burnt sacrifices, Jeremiah is referring to just before Moses went up to Mount Sinai.
If, on the other hand, we are counting God's actual description of the burnt offerings themselves, then Jeremiah was referring to the time when the moral Law was first given, and the people agree to it, before Moses went back up Mount Sinai.