Muwatta Malik 343

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ سَالِمِ بْنِ عَبْدِ اللَّهِ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ أُصَلِّي صَلاَةَ الْمُسَافِرِ مَا لَمْ أُجْمِعْ مُكْثًا وَإِنْ حَبَسَنِي ذَلِكَ اثْنَتَىْ عَشْرَةَ لَيْلَةً ‏.‏

Yahya related to me from Malik from Ibn Shihab from Salim ibn Abdullah that Abdullah ibn Umar used to say, "I pray the prayerof a traveller as long as I am undecided whether to remain somewhere or not, even if I am detained for twelve nights

Reference

Muwatta Malik 343

In-book

Book 9, Hadith 18