Why does it say that Ner Elokim did not yet extinguish?
Radak: This refers to the Neros of the Menorah. They were still burning, for it was before dawn. 1 Afterwards (verse 16), it says that Shmuel slept until the morning.
Radak citing Bereishis Rabah 58:2: This refers to the lamp of prophecy. "V'Zaracht ha'Shemesh u'Va ha'Shemesh" (Kohen 1:5) - Hashem before bringing sunset upon a Tzadik, Hashem raises the sun of another Tzadik. Before the sunset of Moshe, Hashem raised the sun of Yehoshua. Before the sunset of Eli, Hashem raised the sun of Shmuel.
Malbim: The end of the night is optimal for prophecy, for the Nefesh is clean from thoughts of the day, and the brain and all Kelim of thought are purified from the most that clouds them at the beginning of the night.
Was Shmuel sleeping in the Heichal?
Rashi citing Targum Yonasan: No, he was sleeping in Ezras ha'Leviyim, where they guard the Mikdash. Kidushin 78b - the verse must be rearranged 1 [for one may not sit in the Azarah 2 , except for kings of Beis David]! Ner Elokim did not yet extinguish in Heichal Hashem, and Shmuel slept in his place.
Malbim: Intellectually, he lied in the Heichal, i.e. he contemplated the Heichal and Aron. This is like "Gam ba'Laylah Lo Shachav Libo" (Koheles 2:23), "Al Mishkavi ba'Leilos" (Shir ha'Shirim 3:1.
Radak, Malbim: B'Heichal Hashem is Samuch to Terem Yichveh. The Asnachta (which breaks a verse into two sentences) is under "Shochev" (for this complete that matter. The rest of the verse does not teach where he slept.)
Radak: All the more so lying, and all the more so in the Heichal, is forbidden!
